Their houses are nine miles away from each other. Mark rides his bike at a rate of twelve miles per hour. Each hour consists of sixty minutes; therefore I would do 60/12 to get five, representing him being able to do one mile in five minutes. Hence, you shall perform 9*5 or nine times five to get the answer of fourty-five minutes.
12 MILES PER HOUR
60 divided by 12 = 5 minutes
ONE MILE PER 5 MINUTES
9 multiplied by 5 = 45 minutes
I hope this helps.