$\sqrt{\frac{3a}{5b}}=\frac{\sqrt{5b}.\sqrt{3a}}{\sqrt{5b}.\sqrt{5b}}={\frac{\sqrt{15ab}}{5b}}$
$\sqrt{\frac{5x}{18y}}={\frac{\sqrt{5x}.\sqrt{3}}{2\sqrt{3y}.\sqrt{3}}}={\frac{\sqrt{10xy}}{6y}}$
$\sqrt{\frac{4x^3}{25y}}={\frac{2\sqrt{x^3y}}{5y}}$
$\sqrt{\frac{3}{2x^3}}={\frac{\sqrt{6x^3}}{2x^3}}$