Question 26143
Directly related means Cost=k(radius^2)
To find "k" let cost be 6 and r be 7
Then 6=k(7^2)
So, k=6/49
The relating equation is therefore y=(6/49)r^2
So, if the radius is 9-inches the cost will be 
C=(6/49)9^2
Cost=$9.92

Cheers,
stan H.