We can determine the value of the adult ticket cost and student ticket cost by following these steps:
1. solve form one of the variables from one of the equations
Let's solve for a from 2a + 2s = 40
2a + 2s = 40
2a + 2s - 2s = 40 - 2s
2a = 40 - 2s
2a/2 = 40/2 - 2s/2
a = 20 - s
2. Replace the expression found and solve for s
4a + 5s = 87
4(20 - s) + 5s = 87
4×20 - 4×s + 5s = 87
80 - 4s + 5s = 87
80 + s = 87
80 - 80 + s = 87 - 80
s = 7
3. Replace 7 for s into a = 20 - s
a = 20 - 7
a = 13
Then, a = 13 and s = 7.
Then the adult ticket cost is $13 and the student ticket cost is $7