Solve the questions please ????????

Dear student,
Joule is a unit of work and energy. Now by using the formula of work done 
$$\begin{gathered} W = F s(F = force and s = displacement) \\ = Mas (a = acceleration) \\ = Msv/t (v = velocity and t = time) \\ =Ms s/t2 (as velocity is displacement /time) \\ W = M s^2/t^2 =kg{m}^2/s^2 \end{gathered}$$

(ii) Power is defined as work done per unit time

$P=W/t=kg{m}^2{s}^{{}^{-}2}/s=kg{m}^2{s}^{{}^{-}3}$

(iii)  We use the mass and volume of a substance to determine its density. Thus, the units of density are defined by the base units of mass and length.

The density of a substance is the ratio of the mass of a sample of the substance to its volume. The SI unit for density is the kilogram per cubic meter (kg/m³)

Regards