#### Answer

a) $r=60t$
b) $A(r(t))=3600\pi t^{2}$, the area of the circular ripple as a function of time.

#### Work Step by Step

a) Speed of ripple=$\frac{r}{t}=60$
$r=60t$
b) $A(r(t))=\pi r^{2}=\pi (60t)^{2}=3600\pi t^{2}$
This expresses the area of the circular ripple as a function of time.