40 teaspoons is 2 2/3 times 15 teaspoons, so will need to be mixed with 2 2/3 times as much water.
... 2 2/3 × 3 gallons = 8 gallons
8 gallons of water are needed to mix with 40 tsp of weed killer.
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40/15 = 8/3 = 2 2/3
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