Forces and equilibrium — practice question

A car has mass $800\,\text{kg}$. Its engine supplies constant power $P\,\text{kW}$ as the car travels along a straight horizontal road. The resistive force opposing the motion is constant and equal to $R\,\text{N}$. At a speed of $14\,\text{m s}^{-1}$, the car’s acceleration is $1.4\,\text{m s}^{-2}$, and at a speed of $25\,\text{m s}^{-1}$, the acceleration is $0.33\,\text{m s}^{-2}$.