$3$b$.$ The aluminum bar $)=(10\mathrm{.}4{10}^6$ has three loads acting axially as shown. $P_1=1700lb,P_2=1200lb,$ and $P_3=1300lb.$ Here $a=60in,b=24$ in$,$ and $c=36$ in$.$

i$.$ Calculate the change in length of the bar.

ii$.$ To what value should P$3$ be changed to ensure that the bar stays the same length after the loads are applied?