A control rod contains solid boron carbide $(B_{4}C)$ with natural boron. Natural boron consists primarily of two stable isotopes, ${?}^{11}B($with abundance of $80\mathrm{.}1\%)$ and ${?}^{10}B($with abundance of $19\mathrm{.}9\%).$ Determine the total macroscopic cross$-$section and the mean free path. Boron carbide has a density of $2\mathrm{.}52\frac{g}{c}{m}^3.$ Atomic mass of boron and carbon are $10\mathrm{.}81,12\mathrm{.}00$ respectively. ${}_t{(}^{10}(B))=3843b,{}_t{(}^{11}(B))=5\mathrm{.}07b,{}_t{(}^{12}C)=5\mathrm{.}01b\mathrm{.}22P$