In a theater, the first row has 12 seats and each row has 2 more seats than previous row. If the last row has 48 seats, what is the total number of seats in the theater?	Choose the correct option.
A) 550  B) 570  C) 590  D) 610  E) 630
The number of seats in the theater is   12 + (12+2) + ...+ (12+36)=   19(12) + 2(1+2+...+18)=   19(12) + 2(18)(19)/2=   19(12+18) = 19(30) = 570   The answer is 570.
<result>B</result>
In a theater, the first row has 12 seats and each row has 2 more seats than previous row. If the last row has 48 seats, what is the total number of seats in the theater?