Kinematics: The Motion of Particles

A train takes 5 minutes to cover 3km between stations P and Q. Starting from rest at P, it accelerates at a constant rate to a speed of 40km/hr and maintains this speed for a while and then is brought uniformly to rest at Q. If the braking takes three times as long as the accelerate, find the time taken for the train to accelerate.

I worked out that 3000=0*t+0.5at^2+(100/9)*t+0.5a*3t^2+100/9*16t applies to the answer. and t=15s, a= (20/27)ms^-2

but how do you work t and a out?

Million thanks!