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: a man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. the ratio of the speed of the boat in still water and stream is
Options: a. 3: 1, b. 1: 3, c. 2: 4, d. 4: 2, e. none of these
[A]: a

[Q]: Problem: an automobile parts supplier charges $ 25 per package of gaskets. when a customer orders more than 10 packages of gaskets, the supplier charges 4 / 5 the price for each package in excess of 10. during a certain week, the supplier sold 60 packages of gaskets. if 15 percent of the gaskets went to company x, 15 percent to company y, and the rest to company z, what was the total amount, in dollars, that the parts supplier received in payment for the gaskets ?
Options: a. 1340, b. 1445, c. 1375, d. 1415, e. 1455
[A]: a

[Q]: Problem: let s is a set of all natural numbers less than 120 such that hcf of any element in s and 120 is 1. find the sum of all elements in s ?
Options: a. 1584, b. 7640, c. 5640, d. 7240, e. 6780
[A]:
a