It takes Derek 9 minutes to walk a mile if he doesn't have to walk with his brother. If he has to take his brother it takes 12 minutes to walk a mile. How many minutes longer would it take him to walk 20 miles if he had to take his brother?
Alone it would take him 9*20=<T>multiply(9, 20)=180 minutes
With his brother, it would take him 12*20=<T>multiply(12, 20)=240 minutes
240-180=<T>subtract(240, 180)=60 more minutes
