$\frac{6\times 6\times 6\times 6\times 6\times 6}{4\times 4\times 4}=\frac{{{6}^{6}}}{{{4}^{3}}}=\frac{{{6}^{6}}}{{{2}^{6}}}={{\left( \frac{6}{2} \right)}^{6}}={{3}^{6}}$