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.

Ex Input:
Problem: cost is expressed by the formula tb ^ 4. if b is doubled, the new cost w is what percent of the original cost ?
Options: a. w = 200, b. w = 600, c. w = 800, d. w = 1600, e. w = 50

Ex Output:
d

Ex Input:
Problem: after giving a discount of rs. 45 the shopkeeper gets a loss of 10 %, if the cost price is rs. 180. find the markup % ?
Options: a. 0.21, b. 0.2, c. 0.17, d. 0.21, e. 0.15

Ex Output:
e

Ex Input:
Problem: the area of a parallelogram is 288 sq m and its altitude is twice the corresponding base. then the length of the base is ?
Options: a. 12, b. 9, c. 7, d. 6, e. 5

Ex Output:
a