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: the sum of the ages of 5 children born at the intervals of 3 year each is 60 year. what is the age of the youngest child ?
Options: a. 4 year, b. 6 year, c. 10 year, d. none of these, e. 9 year

Answer: b

Question: Problem: a sum of money at simple interest amounts to rs. 720 after 2 years and to rs. 1020 after a further period of 5 years. the sum is :
Options: a. 400, b. 500, c. 600, d. 700, e. 800

Answer: c

Question: Problem: a train moves with a speed of 162 kmph. its speed in metres per second is
Options: a. 10.8, b. 18, c. 30, d. 38.8, e. 45

Answer:
e