If the expression $5^{2 n}-48 n+k$ is divisible by 24 for all $n \in N$, then the least positive integral value of $k$ is

The coefficient of $x y^{2} z^{3}$ in the expansion of $(x-2 y+3 z)^{6}$ is

The set of all real values of $x$ for which the expansion of $\left(125 x^{2}-\frac{27}{x}\right)^{\frac{-2}{3}}$ is valid, is