$(4)$ The pin$-$connected structure shown in the Figure below consists of a rigid bar ABCD and two axial members. Bar $(1)$ is bronze $]$ with a crosssectional area of $A1=620mm2.$ Bar $(2)$ is an aluminum alloy $]$ with a cross$-$sectional area of $A2=340mm2.$ All bars are unstressed before the load $P$ is applied; however, there is a $3-mm$ clearance in the pin connection at $A.$ If a concentrated load of $P=90kN$ acts on the structure at $D,$ determine:

a$.$ the normal stresses in both bars $(1)$ and $(2).$

b$.$ the normal strains in bars $(1)$ and $(2).$

c$.$ the downward deflection of point $D$ on the rigid bar.