In this question, Al drives from York toward Benton and Ben drives from Benton toward York. That means both Al and Ben will reduce the distance between them. In this case, you need to add their velocity. The total velocity should be 45mph+55mph= 100mph
The distance will be shortened by 100mile/hour and the distance is 210 miles. Then the time should be:
time=distance/total velocity =210m/100mph= 2.1 hours
