A$)$ A pre$-$tensioned pre$-$stressed concrete beam having a rectangular section, $150mm$ wide and $300mm$ deep, has an effective cover of $50mm.$ If fck $40\frac{N}{m}{m}^2,ffp=1600\frac{N}{m}{m}^2,$ and the area of pre$-$stressing steel $A=461m{m}^2,$ calculate the ultimate flexural strength of the section