Consider the following two$-$dimensional steady fluid flow, with the velocity field V$($x$,$ y$)=(2$y $+3($x $2$ y $2))$i $+(2$x $36$xy$)$j$,$ where $\{$i$,$j$\}$ are unit basic vectors of the Cartesian system of coordinates in the $($x$,$ y$)$ plane. $($a$)$ Verify that this fluid flow is both incompressible and irrotational, i$.$e$.$ V $=0$ and $$ V $=0.($b$)$ For the above velocity field V$,$ derive the velocity potential and the stream function.