A

For $x\in \mathbb{R}$, $x>0$, simplify the following expression. $$x^3:\sqrt[]{x}$$

Write the number $\sqrt[3]{16000}$ in an equivalent form with smallest possible number under the radical.

Write the fraction $\frac{\sqrt{7}}{\sqrt{3}}$ in an equivalent form which does not contain radical in the denominator.

A body is deformed continuously in a machine press. The density $\rho$ is inversely proportional to the volume $V$ of the body, i.e. there exists a constant $k$ such that $$\rho =\frac{k}{V}.$$ Find the constant $k$ (including the correct unit) if it is known that the density was $\rho =25\frac{\mathrm{kg}}{{\mathrm{m}}^3}$ when the body had volume $V=2{\mathrm{dm}}^3$.