#### Answer

$$3r^2-rs^{\frac{1}{5}}-3rs^{\frac{3}{4}}+s^{\frac{19}{20}}$$

#### Work Step by Step

In order to solve this problem, we may need to use the rules of radicals. Once we have done this, we combine like radicals. Doing this, we find that the expression simplifies to:
$$ \left(r-s^{\frac{3}{4}}\right)\left(3r-s^{\frac{1}{5}}\right)\\ r\cdot \:3r+r\left(-s^{\frac{1}{5}}\right)+\left(-s^{\frac{3}{4}}\right)\cdot \:3r+\left(-s^{\frac{3}{4}}\right)\left(-s^{\frac{1}{5}}\right)\\ 3r^2-rs^{\frac{1}{5}}-3rs^{\frac{3}{4}}+s^{\frac{19}{20}}$$