A bus started out going 20 miles per hour on the highway. One hour later it drove 40 miles per hour on the freeway. How long did it take to go 140 miles? Is the correct answer 3.5 minutes.

No. Have you ever heard of a bus that can go 140 miles in 3.5 minutes? It took an hour just to go the first 20 miles.

You seem to me mixing up hours and minutes, but the answer is not 3.5 hours, either.