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 3.5MILES PER HR??????????
No. They ask for time, not speed.
In the first hour the bus went 20 miles. It needed to go 120 more, at 40 mph. That would take 3 more hours.
The total travel time was 4 hours.