Question $4.$

Rigid bar ABC is supported by a pin at $B$ and by post $(1)$ at A$.$ However, there is a gap of $=10mm$ between the rigid bar at A and post $(1).$ After load $P$ is applied to the rigid bar, point $C$ moves to the left by $8mm.$ If the length of post $(1)$ is $L_1=1\mathrm{.}6m,$ what is the average normal strain that is produced in post $(1)?$ Use dimensions of $a=1\mathrm{.}25m$ and $b=0\mathrm{.}85m.$

Figure $4$