Explanation:
speed = mph or miles/hour
so, when we are dealing with a distance and compare the time spent on the distance, we have to divide distance by speed
miles / miles/hour = hour
so, we have
m/4 + m/3 = 2
as the sum of the time it took to walk the distance at 4mph and the time it took to walk the distance at 3 mph is 2 hours.
now we multiply by the denominators one after the other to eliminate the fractions.
m + 4m/3 = 8
3m + 4m = 24
7m = 24
m = 24/7 = 3.428571429... miles