Michael took the return trip at a velocity 33.75 miles per hour.
Let suppose that Michael drove in straight line road and at constant velocity. Therefore, the speed of the vehicle (v), in miles per hour, can be defined as distance traveled by the vehicle (d), in miles, divided by travel time (t), in hours.
First trip
45 = s / 3 (1)
Second trip
v = s / 4 (2)
By (1) and (2):
45 · 3 = 4 · v
v = 33.75 mi / h
Michael took the return trip at a velocity 33.75 miles per hour.
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