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 garrison of 2000 men has provisions for 54 days. at the end of 18 days, a reinforcement arrives, and it is now found that the provisions will last only for 20 days more. what is the reinforcement ?
Options: a. 1977, b. 1600, c. 1979, d. 1900, e. 1278
b