Calculus problem?

Question

A stone is dropped into a lake, creating a ripple that travels outward at a speed of 60cm/s. find the rate at which the area within the circle is increasing after a. 1s b. 3s, and c. 5s.

Answer 1

Area of a circle of radius R is pi x R^2

So A(t) = pi x R(t)^2

You know R(t) is just (60 cm) x t

So you can compute A'(t)