Mark spent 220 dollars to fix his car.  It needed two parts that cost 20 dollars each, and labor cost .5 dollars a minute. How many hours did the mechanic work?
Labor cost is .5*60=<T>multiply(0.5, 60)=30.0 dollars per hour
The cost for parts is 20*2=$<T>multiply(20, 2)=40
The total cost for labor is 220-40=$<T>subtract(220, 40)=180
He spent 180/30=<T>divide(180, 30)=6.0 hours on labor.
