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.

Example Input: Problem: the dimensions of a room are 25 feet * 15 feet * 12 feet. what is the cost of white washing the four walls of the room at rs. 7 per square feet if there is one door of dimensions 6 feet * 3 feet and three windows of dimensions 4 feet * 3 feet each ?
Options: a. s. 4538, b. s. 6342, c. s. 4518, d. s. 4530, e. s. 4517
Example Output: b

Example Input: Problem: if julie rows 32 km upstream and 72 km down steam taking 4 hours each, then the speed of the stream
Options: a. 1.5 kmph, b. 0.5 kmph, c. 0.4 kmph, d. 1.6 kmph, e. 2.5 kmph
Example Output: b

Example Input: Problem: ? x 12 = 173 x 240
Options: a. 3460, b. 685, c. 865, d. 495, e. 534
Example Output:
a