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: four bells commence tolling together and toll at intervals of 2, 4, 6, 8 seconds respectively. in 18 minutes, how many times do they toll together ?
Options: a. 43, b. 44, c. 45, d. 46, e. 47
[EX A]: c

[EX Q]: Problem: a hiker walking at a constant rate of 4 kilometers per hour is passed by a cyclist travelling in the same direction along the same path at a constant rate of 24 kilometers per hour. the cyclist stops and waits for the hiker 5 minutes after passing her while the hiker continues to walk at her constant rate. how many minutes must the cyclist wait until the hiker catches up ?
Options: a. 10, b. 15, c. 20, d. 25, e. 30
[EX A]: d

[EX Q]: Problem: salad dressing p is made up of 30 % vinegar and 70 % oil, and salad dressing q contains 10 % vinegar and 90 % oil. if the two dressings are combined to produce a salad dressing that is 18 % vinegar, dressing p comprises what percentage of the new dressing ?
Options: a. 20 %, b. 30 %, c. 40 %, d. 50 %, e. 60 %
[EX A]:
c