In this case, we'll have to carry out several steps to find the solution.
Step 01:
Data
total seats = 5000
total revenue = $155600
Step 02:
system of equations:
x = # of $28 tickets
y = # of $40 tickets
equation 1:
x + y = 5000
equation 2:
28x + 40y = 155600
x + y = 5000 * (-28)
28x + 40y = 155600
-28x - 28y = - 140000
28x + 40y = 155600
-----------------------------------
12y = 15600
y = 15600 / 12
y = 1300
y in eq. 1:
x + y = 5000
x + 1300 = 5000
x = 5000 - 13000
x = 3700
The answer is:
x = 3700 of $28 tickets
y = 1300 of $40 tickets