Is this correct?
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If the length is x miles and if the time was y mins... {nl} 5x/6 distance. {nl} 3y/4 time.
Let's say that it was 60 miles, and the drive took an hour. {nl} Then, for 15 mins, they covered 10 miles. {nl} Times 4 for 15 mins and 10 miles. {nl} Thus, the average speed is 40mph. {nl}