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: a trader mixes 80 kg of tea at 15 per kg with 20 kg of tea at cost price of 20 per kg. in order to earn a profit of 25 %, what should be the sale price of the mixed tea ?
Options: a. 23.75, b. 22, c. 20, d. 19.20, e. none of these
[EX A]: c

[EX Q]: Problem: given that p is a positive even integer with a positive units digit, if the units digit of p ^ 3 minus the units digit of p ^ 2 is equal to 0, what is the units digit of p + 4 ?
Options: a. 7, b. 8, c. 10, d. 11, e. 12
[EX A]: c

[EX Q]: Problem: a case contains c cartons. each carton contains b boxes, and each box contains 200 paper clips. how many paper clips are contained in 2 cases ?
Options: a. 200 bc, b. 200 b / c, c. 400 bc, d. 400 b / c, e. 400 / bc
[EX A]:
c