A model for tumor growth is given by the Gompertz equation
$$
\frac{d V}{d t}=a(\ln b-\ln V) V
$$
where $a$ and $b$ are positive constants and $V$ is the volume of the tumor measured in $\mathrm{mm}^{3}$.
(a) Find a family of solutions for tumor volume as a function of time.
(b) Find the solution that has an initial tumor volume of $V(0)=1 \mathrm{~mm}^{3}$