Answer:
 6
Step-by-step explanation:
The largest factor that is common to all these numbers is 6. That is the number of pencil boxes Lana can fill.
 18 = 6×3
 24 = 6×4
 36 = 6×6
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Each of her six (6) pencil boxes will have 3 pencils, 4 erasers, and 6 crayons.