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.

[EX Q]: Problem: a train covers a distance of 100 km in 1 hour. if its speed is decreased by 15 km / hr, the time taken by the car to cover the same distance will be ?
Options: a. 1 hr, b. 1 hr 10 min, c. 50 min, d. 1 hr 30 min, e. 1 hr 45 min
[EX A]: b

[EX Q]: Problem: a and b started a business in partnership investing rs. 20,000 and rs. 15,000 respectively. after 6 months, c joined them with rs. 20,000. whatwill be b ' s share in total profit of rs. 15,000 earned at the end of 2 years from the startingof the business ?
Options: a. s. 5,000, b. s. 4,500, c. s. 5,700, d. s. 6,500, e. s. 7,500
[EX A]: b

[EX Q]: Problem: a plant manager must assign 12 new workers to one of five shifts. she needs a first, second, and third shift, and two alternate shifts. each of the shifts will receive 3 new workers. how many different ways can she assign the new workers ?
Options: a. 2430, b. 2640, c. 3300, d. 4860, e. 5400
[EX A]:
b