Two trains leave town at the same time in opposite direction

Two trains leave town at the same time in opposite directions. One travels at 55 miles per hour and the other travels at 35 miles per hour. In how many minutes will they be 200 miles apart?

At time t = 0 they are together.
They separate at 55 + 35 = 90 mph
How long to travel 200 miles at 90 mph
200/90 = 2.222 hrs or 2 hours 13 minutes roughly