The volume of a metallic cylindrical pipe is 748 cu.cm. Its length is 14 cm & its external radius is 9 cm. How do I find its thickness?

This is what I tried:

pi x r x r x h = 748

pi x r x r x 14 = 748

r x r = 17

r = 4.17 (this is the internal radius)

Now thickness = external radius - internal radius

thickness = 9 - 4.17 = 5.83 cm

But the answer is wrong. Can someone help me out with this?

Thanks,

Ron