If $x * y = x + y + \sqrt{xy}$,the value of $6 * 24$ is

In the following questions,two equations numbered $I$ and $II$ are given. You have to solve both the equations and give the answer.
$I$: $\frac{5}{7} - \frac{5}{21} = \frac{\sqrt{x}}{42}$
$II$: $\frac{\sqrt{y}}{4} + \frac{\sqrt{y}}{16} = \frac{250}{\sqrt{y}}$

Find the smallest number by which $5808$ should be multiplied so that the product becomes a perfect square.

Evaluate $\sqrt{41-\sqrt{21+\sqrt{19-\sqrt{9}}}}$

Given $\sqrt{5}=2.2361$ and $\sqrt{3}=1.7321$,then $\frac{1}{\sqrt{5}-\sqrt{3}} = $

$\sqrt{54} \times \sqrt{2120} \div \sqrt{460} = ?$