Answer :
Question: How long will it take for the two trains to be 420 miles apart if two trains leave at the same time one going east and the other going west, with speed 80 miles per hour and 70 miles respectively. The number of hours to take them to have a distance of 420 can be computed as follows:
Let x= the number of hours
80x+70x=420
150x=420
x=420/150
x=2.8 hours