To solve this problem, we have to find the solution for the set of equations given. This can be done as follows:
y = 5x ( 1 )
12x + 9y = 60 ( 2 )
We substitute (1) to the y in (2).
12x + 9(5x) = 60
12x + 45x = 60
57x = 60
x = 60/57
y = 5(60/57) = 300/57