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: if 12 machine can finish a job in 40 days, then how many more machines would be needed to finish the job in one - fourth less time ?
Options: a. a. 4, b. b. 8, c. c. 10, d. d. 12, e. e. 16
a

Problem: 2,7, 17,3, 11,19, 5,13, __
Options: a. 20, b. 21, c. 22, d. 23, e. 24
d

Problem: an aeroplane covers a certain distance of 420 kmph in 6 hours. to cover the same distance in 4 2 / 3 hours, it must travel at a speed of
Options: a. 440, b. 540, c. 640, d. 740, e. 250

b