For the rectangular beam section shown in Figure $2$ with $f_c^{\text{'}}=30$MPa,$f_y=400$MPa, it is required to:

a$)$ Calculate the required $A_s$ needed, if $M_f=250kN.$m$.$

b$)$ Calculate the required $A_s$ needed, if $M_f=950kN.m.$

c$)$ Draw the cross$-$section designed in $($a$)$ and $($b$)$ above showing the details of the reinforcement according to the standards, assuming $M-{10}_{?}$ stirrups of two branches are used