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: farm tax is levied on the 45 % of the cultivated land. the tax department collected total $ 3840 through the farm tax from the village of mr. willam. mr. willam paid only $ 480 as farm tax. the percentage of total land of mr. willam over the total taxable land of the village is :
Options: a. 15 %, b. 25 %, c. 15.125 %, d. 27.78 %, e. none

Ex Output:
d

Ex Input:
Problem: what is the units digit of 26 ! + 50 ! + 4 ! + 4 ! ?
Options: a. 8, b. 6, c. 4, d. 2, e. 0

Ex Output:
a

Ex Input:
Problem: f ( x ) is a function such that f ( 2 x + 1 ) = 2 f ( x ) + 1 for all real numbers x and f ( 0 ) = 2. find the value of f ( 3 ).
Options: a. 10, b. 11, c. 12, d. 13, e. 14

Ex Output:
b