Give the step-by-step reasoning process and then the final answer. Mary needs school supplies. She has 6 classes and needs 1 folder for each class. She also needs 3 pencils for each class. She decides that for every 6 pencils she should have 1 eraser. She also needs a set of paints for an art class. Folders cost $6, pencils cost $2, and erasers cost $1. If she spends $80, how much did the set of paints cost in dollars?
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Mary needs 6 * 1 = 6 folders. Mary needs 6 * 3 = 18 pencils. Mary needs 18 / 6 = 3 erasers. Mary spends 6 * 6 = $36 on folders. Mary spends 18 * 2 = $36 on pencils. Mary spends 3 * 1 = $3 on erasers. Mary spends 36 + 36 + 3 = $75 on all the supplies except the paints. Mary spends 80 - 75 = $5 on the paint set.
The final answer: 5.
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