Answer:
$319.50
see the procedure
Explanation:
we know that
A relationship between two variables, x, and y, represent a proportional variation if it can be expressed in the form
or

Let
y ---> represents the total cost
x ---> represents the number of months
we have

so
The relationship between x, and y, represent a proportional variation
Complete the table
For x=9 months
substitute the value of x in the linear equation and solve for y
