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 goods train runs at the speed of 72 kmph and crosses a 250 m long platform in 24 seconds. what is the length of the goods train ?
Options: a. 230 m, b. 240 m, c. 260 m, d. 270 m, e. none of these
a

Problem: mary works in a restaurant a maximum of 70 hours. for the first 20 hours, she is paid $ 8 per hour. for each overtime hour, she is paid at a rate which is 25 % higher than her regular rate. how much mary can earn in a week ?
Options: a. 600, b. 620, c. 660, d. 320, e. 400
c

Problem: three numbers are in the ratio 4: 5: 6 and their product is 76680. the largest number is
Options: a. 30, b. 24, c. 26, d. 28, e. 22

b