(a) The area is given by
... A = π·r²
The rate of change of area is the derivative of this with respect to time.
... dA/dt = π·2r·dr/dt
For the given conditions, this evaluates to
... dA/dt = π·2·(5 ft)·(3.5 ft/s) = 35π ft²/s ≈ 109.96 ft²/s
right angle because its always perpendicular to the floor
