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: at a florist shop on a certain day, all corsages sold for either $ 20 or $ 30. if 10 of the corsages that sold for $ 30 had instead sold for $ 20, then the store ' s revenue from corsages that day would have been reduced by 20 percent. what was the store ' s actual revenue from corsages that day ?
Options: a. $ 200, b. $ 400, c. $ 500, d. $ 800, e. $ 1000
[EX A]: c

[EX Q]: Problem: if julie rows 32 km upstream and 72 km down steam taking 4 hours each, then the speed of the stream
Options: a. 1.5 kmph, b. 0.5 kmph, c. 0.4 kmph, d. 1.6 kmph, e. 2.5 kmph
[EX A]: b

[EX Q]: Problem: if y exceeds x by 20 %, then x is less than y by ?
Options: a. 16 2 / 8 %, b. 16 8 / 3 %, c. 16 2 / 3 %, d. 76 2 / 3 %, e. 17 2 / 3 %
[EX A]:
c