Given the following reasoning and answer, what was the question? Ignoring tips, Marta earned $240 - $50 = $190. Therefore, she has worked 190 / 10 = 19 hours.
 The answer: 19

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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The question Marta works on her grandparent's farm to raise money for a new phone. So far, she has collected $240. For every hour she works, she receives $10. Her grandmother often gives her tips, and she has collected $50 in tips in total. How many hours has Marta worked on the farm so far?