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: average expenditure of a person for the first 3 days of a week is rs. 320 and for the next 4 days is rs. 420. average expenditure of the man for the whole week is :
Options: a. 350, b. 370, c. 390, d. 360, e. none
d