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: bill made a profit of 10 % by selling a product. if he had purchased that product for 10 % less and sold it at a profit of 30 %, he would have received $ 63 more. what was his original selling price ?
Options: a. $ 850, b. $ 990, c. $ 1050, d. $ 1180, e. $ 1340
b

Problem: if a train, travelling at a speed of 90 kmph, crosses a pole in 4 sec, then the length of train is ?
Options: a. 281, b. 125, c. 288, d. 100, e. 121
d

Problem: a person x started at 3 hours earlier at 40 km / h from a place p, then another person y followed him at 60 km / h. started his journey at 3 o ' clock, afternoon. what is the diference in time when x was 30 km ahead of y and when y was 30 km ahead of x ?
Options: a. 8 h, b. 3 h, c. 6 h, d. 3 h, e. 1 h

b