The least number that should be multiplied to $3^{20}\times 5^{14}$  to make it a perfect cube  is         

$={\left(3^6\right)}^3\times 3^2\times {\left(5^4\right)}^3\times 5^2$

$\therefore$  Required number$=3\times 5$

To make it a perfect cube multiplied with $\text{15}$