There are three glass cubes of edges $20 \mathrm{~cm}, 16 \mathrm{~cm}$ and $12 \mathrm{~cm}$ respectively. These are melted to form a new cube. Find the edge of the new cube.

(a) $26 \mathrm{~cm}$

(b) $28 \mathrm{~cm}$

(c) $24 \mathrm{~cm}$

(d) $22 \mathrm{~cm}$