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.

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
e

Problem: what is the value of ( 2 ) ^ - 3 ?
Options: a. 1 / 6, b. 1 / 5, c. 1 / 8, d. 1 / 9, e. 1 / 7
c

Problem: marts income is 30 percent more than tims income and tims income is 40 percent less than juans income. what percentage of juans income is marts income
Options: a. 124 %, b. b. 120 %, c. c. 78 %, d. d. 80 %, e. e. 64 %

c