The distance between two cities is one hundred miles and a w

The distance between two cities is one hundred miles, and a woman drives from one city to the other at a rate of fifty mph. At what rate must she return if the total travel time is three hours and forty minutes?

Solution

So far she has traveled for 2 hours
50*2=100
rt=d
r*5/3=100
r=100*3/5
r=60 mph
60*5/3=100
5/3=1 2/3=1 hr 40 min