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.

[Q]: Problem: what will be the compound interest on a sum of rs. 20,000 after 3 years at the rate of 12 % p. a. ?
Options: a. rs. 8098.56, b. rs. 9720, c. rs. 10123.20, d. rs. 10483.20, e. none
[A]: a

[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
[A]: c

[Q]: Problem: if each participant of a chess tournament plays exactly one game with each of the remaining participants, then 276 games will be played during the tournament. find the number of participants.
Options: a. 20, b. 22, c. 24, d. 26, e. 28
[A]:
c