Answer:
55 senior tickets
Explanation:
400 seats
students: $8
Adults: $10
Seniors: $7
All seats were sold and the total money they got was $3,535
Adult tickets sold was 10 less than the # of student and seniors combined.
8a+10b+7c=3535
a+b+c=400 now just solve for them
8a+10b+7c=3535
-8a-8b-8c=-3200
2b-c=335...
If you solve for the numbers, you'll get 55 tickets.