A rod ABCD made of three different cross$-$sections of the same material is under the influence of three axial loads and temperature increase of $30C.$ If the material has coefficient of linear expansion $={15}^{**}\frac{{10}^{-6}}{}C,$ and other characters tics below, calculate

a$)$ Total change in length for the rod

b$)$ The axial stresses at sections $x-x$ and $y-y.$

Use: $A1=600m{m}^2,E=200$Gpa,

$A2=1200m{m}^2,={15}^{**}\frac{{10}^{-6}}{}c,$

$A3=1800m{m}^2,T=30C$