Definition: You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.
Input: Question: A sum of money place at compound interest doubles itself in 6 years. In how many years will it amount to eight times itself?

 Option A: 6

 Option B: 12

 Option C: 18

 Option D: 24

 Option E: 30

Option C