Answer
$\mathrm{CH}_{3} \mathrm{Cl}$ can react with $\mathrm{Cl}$ to form $\mathrm{H}_{2} \mathrm{ClC} ^\cdot$ radical which can react with a $\mathrm{H}_{3} \mathrm{C}^\cdot$ radical to form $\mathrm{ClCH}_{2}\mathrm{CH}_{3}$.
Work Step by Step
See answer above.