Troy is thinking of buying a new computer that is worth $80. He has initially saved $50 and plans to sell his old computer for $20. How much more money does he need so he could buy the new computer? Think carefully first, then make a decision:

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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Troy has $50 + $20 = $70 from his savings and the sales of his old computer. Therefore, he still needs $80 - $70 = $10 more to buy the new computer. So, the answer is 10.