In Exercise, use the formula   You ride your bike to campus a distance of 5 miles and retu...

In Exercise, use the formula   

You ride your bike to campus a distance of 5 miles and return home on the same route. Going to campus, you ride mostly downhill and average 9 miles per hour faster than on your return trip home. If the round trip takes one hour and ten minutes—that is 76 hours—what is your average velocity on the return trip?