$4\mathrm{.}55$ and $4\mathrm{.}56$ Five metal strips, each of $1545-mm$ cross section, are bonded together to form the composite beam shown. The modulus of elasticity is $210$ GPa for the steel, $105$ GPa for the brass, and $70$ GPa for the afuminum. Knowing that the beam is bent about a horizontal axis by couple of moment $1400N*m,$ determine $(a)$ the maximum stress in each of the three metals, $($b$)$ the radius of curvature of the composite beam.