Answer
(a)$$r=60t$$
(b)$$A= 3600 \pi t^2$$
This function represents the area of growing ripple in terms of time.
Work Step by Step
(a) The value of the increasing radius equals the velocity times the elapsed time. So we have $$r=v \times t=60t.$$
(b) $$A= \pi r^2 \quad \Rightarrow$$ $$(A \circ r)(t)=A(r(t))=3600 \pi t^2$$
