splenda-
In your example, the trip is 1 hour, 7.5 minutes, i.e. 67.5 minutes.
The average speed for the round trip is 45 MPH, with half the distance traveled at 60 MPH, half at an unknown MPH and an average MPH of 45.
Traveling 67.5 minutes at an average speed of 45 MPH means the total distance traveled is 50.625 miles.
Half of that distance was at 60 MPH, exactly a mile a minute.
This leaves the other half (25.3125 miles) traveled in 42.1875 minutes (the remaining time).
25.3125 (distance) divided by 42.1875 (minutes) multiplied by 60 gives a MPH of 36.
(btw, nice to have you back here)