$($b$)$ The gas phase reaction $A+\frac{1}{2}B=C$ is carried out isothermally and isobarically. The reaction is first order in $B$ and first order in $A.$ The feed is equal molar in A and $B$ and the entering concentration of $A$ is $0\mathrm{.}5$ movdm $3.$ The specific reaction rate is $k=4\mathrm{.}0dm\frac{3}{m}ol*s.$ Find the value of $(-r_A)$ for $60\%$ conversion of $A,5CO1$