QUESTION $4$: In the system shown, two copper rods AB and CD with a diameter of $15$ mm are fixed to a wall and a rigid plate, along with a steel rod EF with a diameter of $20$ mm $.$ Given that the horizontal displacement at point F of rod EF is $0\mathrm{.}75$ mm under the loading condition shown, determine the magnitude of the force $P.$

$E_{\text{c}\text{o}\text{p}\text{p}\text{e}\text{r}}=100$GPa,$E_{\text{s}\text{t}\text{e}\text{e}\text{l}}=210$GPa