$\sqrt{176+\sqrt{2401}} = ?$

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

$(2 \sqrt{392}-21)+(\sqrt{8}-7)^{2}=(?)^{2}$

If $\sqrt{15625} = 125$,then the value of $\sqrt{15625} + \sqrt{156.25} + \sqrt{1.5625}$ is

What is the value of $\sqrt[3]{0.000064}$?

If $\frac{52}{x} = \sqrt{\frac{169}{289}}$,then the value of $x$ is