If each side of an equilateral triangle is increased by 2 cm, then its area increases by $3 \sqrt{3}$ cm. Find the length of each side.

Question

$\begin{array}{1 1} (a)\; 2\; cm \\ (b)\; 4 \; cm \\ (c)\; 2\sqrt{3} \; cm \\ (d)\; 4 \sqrt{3} \; cm \end{array}$