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: x does a work in 20 days. y does the same work in 40 days. in how many days they together will do the same work ?
Options: a. 10, b. 12, c. 20, d. 30, e. 13.33
[EX A]: e

[EX Q]: Problem: what is the tens digit of 6 ^ 10 ?
Options: a. 7, b. 3, c. 5, d. 1, e. 9
[EX A]: a

[EX Q]: Problem: walking at 5 / 6 th of its usual speed a cab is 15 mnts late. find its usual time to cover the journey ?
Options: a. 25 m, b. 45 m, c. 32 m, d. 75 m, e. 62 m
[EX A]:
d