Mckenna starts her day at 8:00 a.m. She works in her office up to 11:00 a.m. then joins her team of developers at the conference room to talk about projects up to 13:00, from which she works for another two hours and then heads home. How many hours does Mckenna stay at work? Give me reasons, before answering the question

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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From 8:00 to 11:00, Mckenna spends 11:00 - 8:00 = 3 hours at work. When she joins the developers in the conference room for the meeting, she spends an additional 13:00 - 11:00 = 2 hours at work. So far, she has spent 3 + 2 = 5 hours at work. When she works for an additional 2 hours before heading home, her total work hours become 5 + 2 = 7 hours. So the final answer is 7.