A train of weight $200\times 10^{4}$ 
N is running on a horizontal track at a constant speed of 10 m/s, overcoming a constant frictional force of $20\times 10^{3}$ 
N. What is the power of the engine driving the train?
(a) 800kW (b) 1200kW (c) 200kW (d) 400kW