Data
Total number of people = 90
adoult cost = a = $12
child cost = c = $7
total cost = $950
Equations
a + c = 90 (1)
12a + 7c = 950 (2)
Solve equation 1 for a
a = 90 - c
Substitute this equation in equation 2
12(90 - c) + 7c = 950
Solve for c
1080 - 12c + 7c = 950
-5c = 950 - 1080
-5c = -130
c = 26
Calculate the number of adults
a = 90 - 26
a = 64
64 adults visited the museum
