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 10000 liter tank, half - full of water is being filled from a pipe with a flow rate of 1 kiloliter every 2 minutes. at the same time, the tank is losing water from two drains at a rate of 1 kiloliter every 4 minutes and every 6 minutes. how many minutes does it take to fill the tank completely ?
Options: a. 8, b. 12, c. 18, d. 24, e. 60
e

Problem: at garage sale, all of the prices of the items sold were different. if the price of a radio sold at the garage sale was both the 9 th highest price and the 35 th lowest price among the prices of the items sold, how many items were sold at the garage sale ?
Options: a. 43, b. 28, c. 44, d. 49, e. 46
a

Problem: a multiple choice test consists of 4 questions, and each question has 5 answer choices. in how many ways can the test be completed if every question is unanswered ?
Options: a. 24, b. 120, c. 625, d. 720, e. 1024
c