Problem $1(25$ points$)$

For the cross$-$section shown in figure:

a$)$ Determine the bending moment that the reinforced concrete section can carry if $A_s=1200m{m}^2.$

b$)$ Determine the area of the tension steel for an ultimate bending moment of $320kNm.$

$f_a=25\frac{N}{m}{m}^2$

$f_{0}x=500\frac{N}{m}{m}^2$

$d=600mm$

$b=250mm$