To calculate Betty's rate in miles per hour, we need to convert her time from minutes to hours because rate is typically measured in miles per hour.
40 minutes is 2/3 of an hour (since there are 60 minutes in an hour).
To find Betty's rate in miles per hour, we need to divide the distance she drove by the time it took her to drive that distance.
30 miles / (2/3 hour) = 45 miles per hour
Therefore, Betty's rate was 45 miles per hour.