Jake agrees to work part of his debt off.  He owed someone $100 but paid them $40 before agreeing to work off the rest.   He worked for $15 an hour.  How many hours did he have to work?
He has to work off $100-$40=$<T>subtract(100, 40)=60
So he has to work $60/15=<T>divide(60, 15)=4.0 hours
