Step-by-step explanation:
the speed difference is 38 - 23 = 15 mph.
that is the same as one fairy is standing still, and the other is going 15 mph.
so, how long until 15 mph creates a gap of 75 miles ?
remember, speed = distance / time traveled
so,
15 = 75/x
x = 75/15 = 5 hours
after 5 hours they will be 75 miles apart.