A painter is paid 8 dollars per hour and can paint 8 m2 with a roller in this time. Renting a spray gun costs 5 dollars for each hour of use (spraying and cleanup), and the painter can paint 20 m2 per hour with the spray gun. It takes 1/2 an hour for the painter to clean up after using the roller, but 1 hour using the spray gun. You must pay the painter for her time and you must also pay for renting the spray gun for the total amount of time (including cleanup) the spray gun was needed. How much money do you save by using the spray gun on a paint job that involves painting 40 m2.