Problem # $2$:

For the beam shown in the figure, determine the following:

a$.$ Cracking moment for the section shown if $f{c}^{\text{'}}=28$MPa and modulus of rupture of $(40$ Marks$).fr=0\mathrm{.}7\sqrt[\phantom{2}]{?}f{c}^{\text{'}}$

b$.$ Calculate the stress in the concrete at the top and bottom extreme fibers under a positive bending moment of $200kN.$m

$(20$ Marks$).$