Question

the heiht of a cylinder is three times the diameter of the base . The surface area of thre ylinder is 126pi ft^2. What is thr radius of the base?

Answer 1

Surface area = area of two circles (top and bottom) + circumference of the circle times its height.

So, you have:
Surface Area = 2*pi*r^2 + 2*pi*r*h
Surface Area = 2*pi*r^2 + 2*pi*r*6r
Surface Area = 2*pi*r^2 + 12*pi*r^2 = 14*pi*r^2 = 126*pi
=> r^2 = 126/14
=> r^2 = 9
=> r = 3