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: excluding the stoppages, the speed of a bus is 48 km / hr and including the stoppages the speed of the bus is 12 km / hr. for how many minutes does the bus stop per hour ?
Options: a. 45 min, b. 10 min, c. 12 min, d. 20 min, e. 18 min
a

Problem: what is the sum of natural numbers between 30 and 100
Options: a. 4615, b. 4860, c. 5000, d. 5500, e. 5550
a

Problem: average monthly income of a family of 4 earning members was rs. 840. one of the earning members died and therefore, the average income came down to rs 650. the income of the deceased was ?
Options: a. rs. 692.80, b. rs. 820, c. rs. 990, d. rs. 1410, e. none

d