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: a furniture dealer purchased a desk for $ 150 and then set the selling price equal to the purchase price plus a markup that was 40 % of the selling price. if the dealer sold the desk at the selling price, what was the amount of the dealer ' s gross profit from the purchase and the sale of the desk ?
Options: a. $ 40, b. $ 60, c. $ 80, d. $ 90, e. $ 100
e

Problem: find the area of trapezium whose parallel sides are 28 cm and 18 cm long, and the distance between them is 15 cm.
Options: a. 227, b. 299, c. 345, d. 161, e. 212
c