you would want to write this in fraction form. since it takes peter 7 minutes and 30 seconds for one mile the other way to write it would be 7.5/1. that would be your first fraction.
the other fraction would be 15 minutes/x. x represents the number of miles ran in 15 min.
next you would just cross multiply and divide. 15 times one = 15 divided by 7.5=2.
so your answer would be that peter can run 2 miles in 15 min.
hope this helped : )