#### Answer

Total number of seats in theater = 1430

#### Work Step by Step

Number of seats in first Row = 30
Number of seats increase per Row = 2
By formula $a_{n}$ = $a_{1}$ + (n-1)d
Number of seats in $26^{th}$ Row
= 30 + (26 - 1)$\times$2
= 30 + 50
= 80
By formula The sum $S_{n}$ = $\frac{n}{2}$(first term + last term)
Total number of seats in theater
= $\frac{26}{2}$( 30 + 80)
= 13$\times$110
= 1430