what is the number of winning driver's that represented the u.s.?
15
col : date | rnd | race name | circuit | city/location | pole position | winning driver | winning team | report row 1 : 1 | april 8 | autoworks 200 | phoenix international raceway | phoenix, arizona | rick mears | rick mears | team penske | report row 2 : 2 | april 22 | toyota long beach grand prix | streets of long beach | long beach, california | al unser, jr. | al unser, jr. | galles-kraco racing | report row 3 : 3 | may 27 | 74th indianapolis 500 | indianapolis motor speedway | speedway, indiana | emerson fittipaldi | arie luyendyk | doug shierson racing | report row 4 : 4 | june 3 | miller genuine draft 200 | milwaukee mile | west allis, wisconsin | rick mears | al unser, jr. | galles-kraco racing | report row 5 : 5 | june 17 | valvoline grand prix of detroit | streets of detroit | detroit, michigan | michael andretti | michael andretti | newman/haas racing | report row 6 : 6 | june 24 | budweiser/g.i.joe's 200 | portland international raceway | portland, oregon | danny sullivan | michael andretti | newman/haas racing | report row 7 : 7 | july 8 | budweiser grand prix of cleveland | cleveland burke lakefront airport | cleveland, ohio | rick mears | danny sullivan | team penske | report row 8 : 8 | july 15 | marlboro grand prix at the meadowlands | meadowlands sports complex | east rutherford, new jersey | michael andretti | michael andretti | newman/haas racing | report row 9 : 9 | july 22 | molson indy toronto | exhibition place | toronto, ontario | danny sullivan | al unser, jr. | galles-kraco racing | report row 10 : 10 | august 5 | marlboro 500 | michigan international speedway | brooklyn, michigan | emerson fittipaldi | al unser, jr. | galles-kraco racing | report row 11 : 11 | august 26 | texaco/havoline grand prix of denver | streets of denver | denver, colorado | teo fabi | al unser, jr. | galles-kraco racing | report row 12 : 12 | september 2 | molson indy vancouver | streets of vancouver | vancouver, british columbia | michael andretti | al unser, jr. | galles-kraco racing | report row 13 : 13 | september 16 | red roof inns 200 | mid-ohio sports car course | lexington, ohio | michael andretti | michael andretti | newman/haas racing | report row 14 : 14 | september 23 | texaco/havoline 200 | road america | elkhart lake, wisconsin | danny sullivan | michael andretti | newman/haas racing | report row 15 : nc | october 6 | marlboro challenge | nazareth speedway | nazareth, pennsylvania | michael andretti | rick mears | team penske | report row 16 : 15 | october 7 | bosch spark plug grand prix | nazareth speedway | nazareth, pennsylvania | bobby rahal | emerson fittipaldi | team penske | report row 17 : 16 | october 21 | champion spark plug 300k | laguna seca raceway | monterey, california | danny sullivan | danny sullivan | team penske | report
what is the number of winning driver's that represented the u.s.?
Date Rnd Race Name Circuit City/Location Pole position Winning driver Winning team Report
1 April 8 Autoworks 200 Phoenix International Raceway Phoenix, Arizona Rick Mears Rick Mears Team Penske Report
2 April 22 Toyota Long Beach Grand Prix Streets of Long Beach Long Beach, California Al Unser, Jr. Al Unser, Jr. Galles-Kraco Racing Report
3 May 27 74th Indianapolis 500 Indianapolis Motor Speedway Speedway, Indiana Emerson Fittipaldi Arie Luyendyk Doug Shierson Racing Report
4 June 3 Miller Genuine Draft 200 Milwaukee Mile West Allis, Wisconsin Rick Mears Al Unser, Jr. Galles-Kraco Racing Report
5 June 17 Valvoline Grand Prix of Detroit Streets of Detroit Detroit, Michigan Michael Andretti Michael Andretti Newman/Haas Racing Report
6 June 24 Budweiser/G.I.Joe's 200 Portland International Raceway Portland, Oregon Danny Sullivan Michael Andretti Newman/Haas Racing Report
7 July 8 Budweiser Grand Prix of Cleveland Cleveland Burke Lakefront Airport Cleveland, Ohio Rick Mears Danny Sullivan Team Penske Report
8 July 15 Marlboro Grand Prix at the Meadowlands Meadowlands Sports Complex East Rutherford, New Jersey Michael Andretti Michael Andretti Newman/Haas Racing Report
9 July 22 Molson Indy Toronto Exhibition Place Toronto, Ontario Danny Sullivan Al Unser, Jr. Galles-Kraco Racing Report
10 August 5 Marlboro 500 Michigan International Speedway Brooklyn, Michigan Emerson Fittipaldi Al Unser, Jr. Galles-Kraco Racing Report
11 August 26 Texaco/Havoline Grand Prix of Denver Streets of Denver Denver, Colorado Teo Fabi Al Unser, Jr. Galles-Kraco Racing Report
12 September 2 Molson Indy Vancouver Streets of Vancouver Vancouver, British Columbia Michael Andretti Al Unser, Jr. Galles-Kraco Racing Report
13 September 16 Red Roof Inns 200 Mid-Ohio Sports Car Course Lexington, Ohio Michael Andretti Michael Andretti Newman/Haas Racing Report
14 September 23 Texaco/Havoline 200 Road America Elkhart Lake, Wisconsin Danny Sullivan Michael Andretti Newman/Haas Racing Report
NC October 6 Marlboro Challenge Nazareth Speedway Nazareth, Pennsylvania Michael Andretti Rick Mears Team Penske Report
15 October 7 Bosch Spark Plug Grand Prix Nazareth Speedway Nazareth, Pennsylvania Bobby Rahal Emerson Fittipaldi Team Penske Report
16 October 21 Champion Spark Plug 300K Laguna Seca Raceway Monterey, California Danny Sullivan Danny Sullivan Team Penske Report
15