Algebra about trains

Question

Two trains leave a station at 11 am onetrain travels north at a rate (speed) of 36mph and another travels east at a rate (speed) of 48 mph. Assuming that the trains do not stop, at what time will the trains be  90 miles apart?

Answer 1

This is a 3-4-5 triangle problem.

At any point in time the trains will be 60t miles apart.

Therefore, at t=1.5, they will be 90 miles apart.