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: in what time will a train 120 m long cross an electric pole, it its speed be 121 km / hr ?
Options: a. 2.5, b. 2.7, c. 2.9, d. 3.6, e. 2.1

Answer: d


Question: Problem: a student travels from his house to school at 12 km / hr and reaches school 2 hours late. the next day he travels 20 km / hr and reaches school 1 hour early. what is the distance between his house and the school ?
Options: a. 90, b. 100, c. 110, d. 120, e. 130

Answer: a


Question: Problem: the avg weight of a, b & c is 84 kg. if d joins the group, the avg weight of the group becomes 80 kg. if another man e who weights is 8 kg more than d replaces a, then the avgof b, c, d & e becomes 79 kg. what is the weight of a ?
Options: a. 25, b. 35, c. 75, d. 80, e. 90

Answer:
d