Martin needs 3.25 gallons of red paint for his small barn and 1.25 gallons of paint for his shed. He spends $81 on paint. How much does the paint cost per gallon?

Martin buys 3.25 + 1.25 = 4.5 gallons of paint altogether. Divide the total cost, $81, by 4.5 gallons: $81 ÷ 4.5 = $18 per gallon. The paint costs $18.00 per gallon.

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