Within a $2$D flow field, fluid velocity is described by V $=($x$^2$ y$^2+$xt$^2)$i $(3$xyt $+$ y$)$j ft$/$s$.$At $($x$,$ y$)=(2\mathrm{.}5$ ft$,3\mathrm{.}5$ ft$)$ at t $=3$ s$,$ find $($a$)$ the magnitude of the fluid particle velocity and its

angle from the x$-$axis,