Q: Elise is buying more dog food. She buys a 15kg bag then another 10kg bag, and she now has 40kg of dog food. How many kilograms of dog food did Elise already have?
A: 15
Explain how we arrive at this answer:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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Explanation: Elise has bought a total of 15 kg + 10 kg = 25kg of dog food. This means she already had 40 kg – 25 kg = 15kg of dog food.