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 group of hikers is planning a trip that will take them up a mountain using one route and back down using another route. they plan to travel down the mountain at a rate of one and a half times the rate they will use on the way up, but the time each route will take is the same. if they will go up the mountain at a rate of 7 miles per day and it will take them two days, how many miles long is the route down the mountain ?
Options: a. 18, b. 19, c. 20, d. 21, e. 22
d

Problem: the size of a television screen is given as the length of the screen ' s diagonal. if the screens were flat, then the area of a square 19 - inch screen would be how many square inches greater than the area of a square 17 - inch screen ?
Options: a. 36, b. 4, c. 16, d. 38, e. 40
a

Problem: the total marks obtained by a student in mathematics and physics is 30 and his score in chemistry is 20 marks more than that in physics. find the average marks scored in mathamatics and chemistry together.
Options: a. 40, b. 30, c. 25, d. data inadequate, e. none of these.

c