A spherical metal ball whose radius is $21\; cm$ is melted to make smaller balls each of radii $0.7\; cm$. How many balls can be made from the bigger ball ?

Question

$\begin{array}{1 1} (a)\; 270 \\ (b)\; 2700 \\ (c)\; 27,000 \\ (d)\; 270,000 \end{array}$