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 Q]: Problem: if the sides of a triangle are 26 cm, 24 cm and 15 cm, what is its area ?
Options: a. 120, b. 772, c. 180, d. 266, e. 2848
[EX A]: c

[EX Q]: Problem: if the average ( arithmetic mean ) of a and b is 45 and the average of b and c is 80, what is the value of c − a ?
Options: a. 25, b. 60, c. 90, d. 140, e. it can not be determined from the information given.
[EX A]: b

[EX Q]: Problem: farm tax is levied on the 25 % of the cultivated land. the tax department collected total $ 3840 through the farm tax from the village of mr. william. mr. william 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. 50 %, d. 0.2083 %, e. none
[EX A]:
c