Question 1140539
Assume it went up 25 miles, so it took an hour
It came down in 1/3 of an hour, so 50 miles took 4/3 hours or 37.5 mph

It comes down 3 times faster than it goes up, so the increased speed coming down is applied only 1/3 as much
3/4 of the time (1 hour/1 1/3 hours) it is going 25 mph and 1/4 of the time 75 mph
(3/4)*25+(1/4)75=37.5 mph