Problem $3$: Three rods$/$cylinders are connected and placed between two rigid walls. If the rods were installed at $12$ degrees $C$ and the temperature is increased to $18$ degrees $C,$ what would be the total force exerted on the walls? Details on the assembly are below.

Steel

Brass

Copper

$E_{st}=200$GPa,$E_{br}=100$GPa,$E_{cu}=120$GPa

${}_{st}=12\frac{{10}^{-6}}{C}C,{}_{br}=21\frac{{10}^{-6}}{}C,{}_{cu}=17\frac{{10}^{-6}}{}C$