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: what is the rate percent when the simple interest on rs. 720 amount to rs. 180 in 4 years ?
Options: a. 6.25, b. 7.25, c. 8.25, d. 9.25, e. 10.25
[EX A]: a

[EX Q]: Problem: 108 a 108 + 92 a 92 = ?
Options: a. 20120, b. 11500, c. 20128, d. 20660, e. 20228
[EX A]: c

[EX Q]: Problem: what will be the compound interest on a sum of rs. 28,000 after 3 years at the rate of 12 % p. a. ?
Options: a. s. 10123.77, b. s. 10123.21, c. s. 10123.20, d. s. 10123.28, e. s. 11337.98
[EX A]:
e