Karl bought a lawn mower for $450, and he charges customers $20 each to mow their lawns. he uses approximately $2 in gas for each lawn that he mows. how many lawns must he mow to break even?

You have to divide 450 by 18 because that's how much money he makes per every lawn he mows, $20 is the amount he's paid minus $2 because he spends that much on gas per lawn mowed. Therefor you get 25