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: by investing in 1623 % stock at 64, one earns rs. 1600. the investment made is
Options: a. s. 9600, b. s. 7500, c. s. 5640, d. s. 6144, e. s. 6760
d