She is going 66 miles per hour.
As you know, speed is usually measured in miles per hour. The distance between the 88 mile marker and the 121 mile marker is 33 miles. That means Sara’s mom travelled 33 miles in 30 mins. You want to figure out how many miles she travelled in 60 minutes.
If she travelled 33 miles in 30 minutes, and 60 minutes is double 30 minutes, then Sara’s mom was traveling 66 miles per hour.
