Give the step-by-step reasoning process and then the final answer. A farmer has 51 cows. The farmer adds five new cows to its herd and then sells a quarter of the herd. How many cows does the farmer have left?

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 farmer has 51 + 5 = 56 cows in its herd. The farmer sells 56 / 4 = 14 cows of the herd. The farmer now has 56 - 14 = 42 cows.
The final answer: 42.