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: vehicle x is 22 miles ahead of vehicle y, which is traveling the same direction along the same route as vehicle x. if vehicle x is traveling at an average speed of 36 miles per hour and vehicle y is traveling at an average speed of 45 miles per hour, how long will it take vehicle y to overtake and drive 23 miles ahead of vehicle x ?
Options: a. 5 hours, b. 7 hours 20 minutes, c. 4 hours, d. 3 hours 45 minutes, e. 2 hours 30 minutes
a

Problem: a girl scout was selling boxes of cookies. in a month, she sold both boxes of chocolate chip cookies ( $ 1.25 each ) and boxes of plain cookies ( $ 0.75 each ). altogether, she sold 1,585 boxes for a combined value of $ 1, 588.25. how many boxes of plain cookies did she sell ?
Options: a. 0, b. 233, c. 500, d. 695, e. 786
e