At constant acceleration , after time t, the speed will be . You say "the first part" but you don't say what the time is or if "the first part" is the same length of the time as the other "parts". The graph of that is a straight line with slope . Calling the length of time for the first part " ", the velocity at the end of the first part will be which, presumably, is the constant speed of the "second part". Taking the length of time for the "second part" " , the second part of the graph is ahorizontalstraight line with height V, from to . The third part of the graph will be a straight line with slope . Of course, the train will stop after time interval where

I don't uderstand what the "it travel constant velocity with the of the total time" means. You did not mention "t" before and 4/3 is larger than 1.