Calculus rate of change problems

Hello, so I need help with a few problems concerning rate of change and implicit differentiation.

Here is the problem. If you are bored, I will be posting more problems tonight so you can check my Q/A for more :)

Oil is leaking to form a circular pattern.The radius of the oil leak is increasing at a rate of 2 inches per minute. How fast is the area of the spot changing when the radius is 6 inches?

Thanks for your time in advance!!

A= pi r^2

We are given dr/dt = +2inch/min

We want how area changes with time (i.e. dA/dt)

dA/dt= dA/dr * dr/dt [ the dr's "cancel" out]

dA/dt = (2 pi r ) * 2 = 4 pi r

When r=6, dA/dt = 4 pi * 6 = 24 pi inches/minute.