Where do I start?

Question

Let A be the area of a circle with radius r. If dr/dt=3, find dA/dt when r=5.

So I know to use the equation A=(pi)r^2 but, I don't know where to go from there. Do I plug in 5 for r and solve?

Answer 1

here

A= ∏r²

dA/dt = ∏*2*r * dr/dt

=> dA/dt = 2∏*5*3

=>dA/dt = 30∏