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: dropbox charges $ 3.10 for first 1 / 5 of a month for 500 gb storage, plus $ 0.40 for each additional 1 / 5 of a month. what would dropbox charge for a data storage of 500 gb for 8 months ?
Options: a. $ 15.60, b. $ 16.00, c. $ 17.80, d. $ 18.70, e. $ 19.10
[A]: d


[Q]: Problem: the ratio of the volumes of two cubes is 1331: 2197. what is the ratio of their total surface areas ?
Options: a. 121: 169, b. 169: 122, c. 81: 124, d. 81: 126, e. 81: 129
[A]: a


[Q]: Problem: a can do a work in 6 days, b can do a work in 8 days and c can do it in 12 days. b left work after 5 days. for how many number of days should a and c should work together to complete the remaining work ?
Options: a. 1 / 2, b. 2 / 3, c. 3 / 4, d. 4 / 3, e. 5 / 2
[A]:
b