Marks$)$: Determine the largest load P that can be applied on the frame shown in Figure $(1)$without causing either the average normal stress or the average shear stress at section aa to exceed $\backslash (\backslash$sigma$=150\backslash$mathrm$\{$MPa$\}\backslash )$and $\backslash (\backslash$tau$=60\backslash$mathrm$\{$MPa$\}\backslash )$respectively$.$ Member CB has a square cross section of $25$mm on each side.