In a theater, the first row has 14 seats and each row has 2 more seats than previous row. If the last row has 56 seats, what is the total number of seats in the theater?
Choose one:
A) 770 B) 780 C) 790 D) 800 E) 810
The number of seats in the theater is   14 + (14+2) + ...+ (14+42)=   22(14) + 2(1+2+...+21)=   22(14) + 2(21)(22)/2=   22(14+21) = 22(35) = 770   The answer is 770.
<result>A</result>
In a theater, the first row has 14 seats and each row has 2 more seats than previous row. If the last row has 56 seats, what is the total number of seats in the theater?