Let n = the hours elapsed when the two trains are 660 miles apart.
Let the first train travel east and the second train travel west.
The distance traveled by the first train is
x = (50 mi/h)*(n h) = 50n mi
The distance traveled by the second train is
y = (60 mi/h)*(n h) = 60n h
The distance between the two trains after n hours is
x + y = 50 n + 60n = 110n mi
Because this distance is 660 miles, therefore
110n = 660
n = 6 hours
Answer: 6 hours
I hope this helps. Sorry it took so long
