What should come in place of the question mark $(?)$ in the following equation?
$30.01^{2} - 19.98^{2} - ? = 21.81^{2}$

What will come in the place of the question mark $(?)$ in the following expression?
$\sqrt{15^{2} \times 12 \div 9 - 125 + 21} = ?$

$A$ sum of $Rs. 1360$ has been divided among $A, B$ and $C$ such that $A$ gets $\frac{2}{3}$ of what $B$ gets and $B$ gets $\frac{1}{4}$ of what $C$ gets. $B$'s share is (in $Rs.$)

If $P = \frac{(\sqrt{7} - \sqrt{6})}{(\sqrt{7} + \sqrt{6})},$ then what is the value of $\left(P + \frac{1}{P}\right)?$

If $\frac{x}{y} = \frac{3}{4},$ the ratio of $(2x + 3y)$ and $(3y - 2x)$ is

If $x = (0.25)^{\frac{1}{2}}, y = (0.5)^{2}, z = (0.216)^{\frac{1}{3}},$ then