The age difference between Beth and her sister is 18 - 5 = 13 years. Beth must be 13 x 2 = 26 to be twice her sister's age. Beth will be twice her sister's age in 26 - 18 = 8 years.is the reasoning for what question and answer pair?

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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Q: If Beth is 18 years old and her little sister is 5, in how many years would she be twice her sister's age?
A: 8