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.
--------
Question: Problem: a train of length 250 m crosses a bridge of length 150 m in 20 seconds. what is the speed of train ?
Options: a. 33, b. 27, c. 25, d. 22, e. 72

Answer: e


Question: Problem: an assembly line produces 15 cogs per hour until an initial order of 60 cogs is completed. the speed of the assembly line is then immediately increased so that it can produce 60 cogs per hour until another 60 cogs are produced. what is the overall average output, in cogs per hour, for the assembly line during this whole time ?
Options: a. 20, b. 22, c. 24, d. 26, e. 28

Answer: c


Question: Problem: a bookseller sells his books at a 20 % markup in price. if he sells a book for $ 36.00, how much did he pay for it ?
Options: a. $ 34.40, b. $ 34.00, c. $ 32.00, d. $ 30.00, e. $ 35.00

Answer:
d