The part of a tree normally sawed into lumber is the trunk, a solid shaped approximately like a right circular

The part of a tree normally sawed into lumber is the trunk, a solid
shaped approximately like a right circular cylinder. If the radius of
the trunk of a certain tree is growing 1/2 inch per year and the height is
increasing 8 inches per year, how fast is the volume increasing when
the radius is 20 inches and the height is 400 inches? Express your
answer in board feet per year (1 board foot = 1 inch by 12 inches by
12 inches).

How do you set this up using the chain rule? I can solve it if I knew how to set it up.

Use the formula for volume of a right circular cylinder:

V = π r²h

Differentiate both sides with respect to t:

dV/dt = (∂V/∂r)(dr/dt) + (∂V/∂h)(dh/dt)
  = (2π rh)(dr/dt) + (π r²)(dh/dt)

Now just evaluate the right side using the given values of r, h, dr/dt, and dh/dt.. This answer will be in cubic inches per year. To convert to board feet per year, divide by 144.