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.

[EX Q]: Problem: points a, b, c, and d, in that order, lie on a line. if ab = 3 cm, ac = 4 cm, and bd = 8 cm, what is cd, in centimeters ?
Options: a. 7, b. 2, c. 3, d. 4, e. 5
[EX A]: a

[EX Q]: Problem: cost is expressed by the formula tb ^ 4. if b is doubled, the new cost w is what percent of the original cost ?
Options: a. w = 200, b. w = 600, c. w = 800, d. w = 1600, e. w = 50
[EX A]: d

[EX Q]: Problem: workers decided to raise rs. 3 lacs by equal contribution from each. had they contributed rs. 50 eachextra, the contribution would have been rs. 3.75 lacs. how many workers were they ?
Options: a. 220, b. 230, c. 500, d. 1500, e. 590
[EX A]:
d