The position function of a particle is $$r$($t$)=3\mathrm{.}0$t$3^$i$+4\mathrm{.}0^$j$.$r$($t$)=3\mathrm{.}0$t$3$i$^+4\mathrm{.}0$j$^.($a$)$ What is the instantaneous velocity at t $=3$ s$?($b$)$ Is the average velocity between $2$ s and $4$ s equal to the instantaneous velocity at t $=3$ s$?$