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: a, b, c can complete a piece of work in 24, 8,12 days. working together, they complete the same work in how many days ?
Options: a. 4, b. 4 / 5, c. 7 / 9, d. 10, e. 24 / 7
a

Problem: two trains of length 100 meters and 200 meters are 450 meters apart. they are moving towards each other on parallel tracks, at speeds of 90 km / h and 72 km / h. after how many seconds will the trains meet ?
Options: a. 6, b. 8, c. 10, d. 12, e. 14
c

Problem: the total price of a basic computer and printer are $ 2,500. if the same printer had been purchased with an enhanced computer whose price was $ 500 more than the price of the basic computer, then the price of the printer would have been 2 / 5 of that total. what was the price of the basic computer ?
Options: a. 1300, b. 1600, c. 1750, d. 1900, e. 2000
a