There are 1080 seats in the theater.
We know that the students filled 702 seats, leaving 35% vacant.
Then 702 seats represents the (100% - 35% = 65%) of the total number of seats.
So, if the total number of seats is S, we can write:
(65%/100%)*S as the 65% of S.
Then we solve:
(65%/100%)*S = 702
0.65*S = 702
S = 702/0.65 = 1,080
There are 1,080 seats in the theater.