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 is the smallest number by which 2880 must be divided in order to make it into a perfect square ?
Options: a. 3, b. 4, c. 5, d. 6, e. 7
[A]: c


[Q]: Problem: what is the rate percent when the simple interest on rs. 810 amount to rs. 155 in 4 years ?
Options: a. 4.78, b. 4.68, c. 4.58, d. 4.48, e. 4.38
[A]: a


[Q]: Problem: one fast typist type some matter in 4 hrs and another slow typist type the same matter in 6 hrs. if both do combine in how much time they will take to finish.
Options: a. 10 hr, b. 1 hr, c. 2 hr 24 mins, d. 3 hr 4 mins, e. 4 hr 10 mins
[A]:
c