I'm going to try to help you out with your threads, but it's almost too time consuming to download and open the question. The stem states that it took 25 hours to arrive at the station W. It gives you distance from one station to the other at rate of 50mph. So the total distance is 50 x 25 = 1250 miles.

Now, all you have to do is add the station distance. you know that both station will meet at V to W, 750 miles. So from start point to V needs to be 1250 - 750 = 500, therefore U to V is the correct answer.

Yeah the train started at U.