A train takes 5 minutes to cover a distance of 3km between two stations P and Q. Starting from rest at P, it accelerates at a constant rate to a speed of 40kmh^(-1) and maintains this speed until it is brought uniformly to rest at Q. If the train takes three times as long to decelerate as it does to accelerate, find the time taken by the train to accelerate. Draw a velocity time graph for the journey of the train.