Problem $3.(30$ points$)$

The reinforced concrete beam shown is subjected to a positive bending

moment of $175kN.m,$ knowing that modulus of elasticity is $25$ GPa for

the concrete and $200$ GPa for the steel, determine

$($a$)$ stress in steel,

$($b$)$ the maximum stress in the concrete. $(=3\mathrm{.}14)$