P$5\mathrm{.}19$ Three bars, each with a cross$$sectional area of $750$ mm$2$ and a length of $5\mathrm{.}0$ m$,$ are connected and loaded as shown in Figure P$5\mathrm{.}19.$ Bars $(1)$ and $(3)$ are made of steel $[$E $200=$ GPa$]$ and bar $(2)$ is made of an aluminum alloy $[$E $=70$ GPa$].$ At D$,$ all three bars are connected to a slider block that is constrained to travel in a smooth, horizontal slot. When the load P is applied, the strain in bar $(2)$ is found to be $0\mathrm{.}0012$ mm$/$mm$.$ Assume that a $=2\mathrm{.}4$ m and b $=1\mathrm{.}6$ m$.$ Determine

$($a$)$ the horizontal deflection of D$.$

$($b$)$ the deformations in each of the three bars.

$($c$)$ the magnitude of load P$.$