Answer:
$450
Step-by-step explanation:
First, find an equation that represents the proportional relationship between number of months (x) and amount spent (y).
A proportional equation can be represented in the form, y = kx, where,
k = constant of proportionality = y/x
Using a point on the line, (1, 50),
k = 50/1 = 50.
Substitute k = 50 into y = kx
The equation would be:
y = 50x
After 9 months (x), they would pay the following:
Substitute x = 9 into y = 50x
Thus:
y = 50(9)
y = 450