Question 9317
The express overtakes the freight train when distance = distance, or in other words when {{{r*t = r*t}}}.  Let x = time of the express to overtake the freight train.  Then x+2 = time of the freight train (since it is slower, the time is greater than the express),


30(x+2) = 50(x)
30x + 60 = 50x


Subtract 30x from each side:
30x - 30x + 60 = 50x - 30x
60 = 20x
3 = x 


The express overtakes the freight train 3 hours after it left at 7 a.m., which you correctly said is at 10 am.


R^2 at SCC