Final answer:
Tom must earn at least $160 before taxes to have a positive cash flow after paying $120 for the painter, due to being in the 25% tax bracket.
Step-by-step explanation:
To calculate the minimum amount Tom must earn for a positive cash flow after hiring a painter and accounting for taxes, we need to establish the break-even point. Since Tom is in the 25% marginal tax bracket, he will take home 75% of his earnings after tax. The painter costs $120, so we divide this amount by 0.75 to determine the pre-tax amount that Tom needs to earn to cover this cost.
The calculation would be as follows:
120 / 0.75 = $160
Therefore, Tom must earn at least $160 before taxes to have a positive cash flow after paying the painter.