So. We know that Mike paid 71 dollars. We also know that NO MATTER WHAT. He has to pay 17 dollars. So 71-17 is 64. Now, all we need to do is divide 64 dollars, by 6 dollars, to give us the number of hours.
64/6 = 10.6
So Mike had the bike for 10.6 (approxamently) hours.