2 hours
Step-by-step explanation:
We know the van moves at 40 miles per hour.
In 2 hours of driving, the van reaches 80 miles.
We have to get to 100 miles driven.
Now, there are 20 miles left to 100.
Let's split the number 40 driven in one hour to 20 miles driven in 30 minutes.
Now, we have 2 and 1/2 hours. It is the answer.