$3$J$1$ For the double$-$web T$-$section beam shown in Figure $1$ with $f_c^{\text{'}}=35$MPa,$f_y=400$MPa, it is required to

a$)$ Sketch the equivalent single$-$web T$-$section beam.

b$)$ Calculate cracking moment $(M_{cr})$ for the beam section considering reinforcement.

c$)$ Calculate cracking moment $(M_{cr})$ for the beam section neglecting reinforcement.

d$)$ Evaluate, in percentages, the increase in the $(M_{cr})$ between the two cases $.$