You will be given a definition of a task first, then some input of the task.
Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

Problem: if the simple interest on a certain sum of money for 2 years is one – fifth of the sum, then the rate of interest per annum is
Options: a. 14 %, b. 7 %, c. 10 %, d. 15 %, e. 3 %
Output:

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.
user
c