$($a$)$ A person walks at $4\mathrm{.}0$ km$/$h for $5\mathrm{.}0$ km$,$ then at $6\mathrm{.}0$ km$/$h for an equal time. Find the average velocity. $($b$)$ A person walks at $4\mathrm{.}0$ km$/$h for $5\mathrm{.}0$ km$,$ then at $6\mathrm{.}0$ km$/$h for an equal distance. Find the average velocity. $[$Ans: $5\mathrm{.}0$ km$/$h$,4\mathrm{.}8$ km$/$h$]$