Give the step-by-step reasoning process and then the final answer. Mr. Alonzo harvested 245.5 kg of tomatoes. He sold 125.5 kg to Mrs. Maxwell and 78 kg to Mr. Wilson. How many kilograms of tomatoes are not sold?

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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Mr. Alonzo was able to sell 125.5 + 78 = 203.5 kg of tomatoes. So, there are 245.5 - 203.5 = 42 kg unsold tomatoes.
The final answer: 42.