Question 703193
Maybe you could organize your calculations in a table,
maybe with columns for painting time, cleaning time, total time, labor cost, rental cost, and total cost.
 
Roller option:
Painting time = (40 m^2)/(8 m^2/hour) = 5 hours.
Clean-up time = 0.5 hours.
Total time = 5 hours + 0.5 hours = 5.5 hours
Labor cost = (5.5 hours)($9/hour) = $49.50
Rental cost = $0
Total cost = $49.50
 
Spay gun option:
Painting time = (40 m^2)/(20 m^2/hour) = 2 hours.
Clean-up time = 1 hour.
Total time = 2 hours + 1 hour = 3 hours
Labor cost = (3 hours)($9/hour) = $27
Rental cost = (3 hours)($5/hour) = $15
Total cost = $27 + $15 = $42
 
Money saved = $49.50 - $42 = $7.50