Not quite there. You’re just adding two different MPH figures and getting an average of the two. But, if you drove one mile at 30 MPH, it would take you 2 minutes, or 120 seconds. If you drove that same mile back at 90 MPH, it would take you 40 seconds. For a grand total of 160 seconds to drive 2 miles. That is an average of 80 seconds per mile or 45 MPH.
It’s easier to realize at a distance of 60 miles each direction. To average 60 MPH, you would have to make the round trip in two hours (120 miles/2 hours = 60MPH). But the first 60 miles took you two hours to drive at 30 MPH. That leaves no time for the return trip. There is no solution.
No Time Left For You
The Guess Who
1969
https://www.youtube.com/watch?v=NPX48NpSRvo
Why isn’t infinite speed a solution? At infinite speed, your return trip time would be zero and you would have averaged 60.
I suppose you are now going to argue about the Special Theory of Relativity, C, And all those picayune annoyances.