Question 167225
d=r*t

d=r*t in terms of the express train is 600=(r+20)t where r is the rate of freight train.  remember time is equal in both cases as stated in the problem.

d=r*t in terms of the freight train is 360=rt

{{{600=rt+20t}}}
{{{360=rt}}}............subtract the 2nd equation from the 1st and you get

{{{240=20t}}}---->{{{t=12}}} which is the same for both trains

rate of the freight is 360/12{{{highlight(freight=30mph)}}}
rate of the express is 30+20{{{highlight(express =50mph)}}}