Definition: 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.
Input: Problem: a square mirror has exactly half the area of the rectangular wall on which it is hung. if each side of the mirror is 21 inches and the width of the wall is 28 inches, what is the length of the wall, in inches ?
Options: a. 21.5, b. 31.5, c. 41.5, d. 61.5, e. 71.5
Output:
b