Problem $20.$ The velocity profile in fully developed laminar flow in a circular pipe of inner radius R $=3$ cm$,$ is given by u$($r$)=9(1$ r $2/$R$2)$ in m$/$s$.$ What is the volume flow rate? $($a$)0\mathrm{.}0085$ m$3/$s $($b$)0\mathrm{.}0101$ m$3/$s $($c$)0\mathrm{.}0112$ m$3/$s $($d$)0\mathrm{.}0127$ m$3/$s $($e$)$ None of these.