###Human: 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?, ### Assistant: Labor cost is .5*60=30 dollars per hour
The cost for parts is 20*2=$40
The total cost for labor is 220-40=$180
He spent 180/30=6 hours on labor. 
 So the answer is :  6