To maintain a speed of 80 km/h by a bus of mass 500 kg on a plane rough road for 4km distance, the work done by the engine of the bus will be ___ kJ. [The coefficient of friction between tyre of bus and road is 0.04], $\mathrm{take} \mathrm{g}=9.8 {\mathrm{ms}}^{-2}$]