Answer:
My answer would be 408 seats i think
Explanation:
what i did was...
21*18=368
r1- +2
r2- +2
r3- +2
r4 - +2
r5- +2
r6- +2
r7-+2
r8- +2
r9- +2
r10- +2
r11- +2
r12- +2
r13- +2
r14- +2
r15- +2
r16- +2
r17- +2
r18- +2
r19- +2
r20- +2
r21- +2 all those 2's together is 40
368+40= 408