You will be given a definition of a task first, then some input of the task.
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: a salesman ' s terms were changed from a flat commission of 5 % on all his sales to a fixed salary of rs. 1000 plus 2.5 % commission on all sales exceeding rs. 4,000. if his remuneration as per new scheme was rs. 600 more than that by the previous schema, his sales were worth ?
Options: a. 12002, b. 12000, c. 12028, d. 12020, e. 12013
Output:
b