Devante has a lunch account in the school cafeteria. His starting balance at the beginning of the month in $35.50. The first week, Devante bought 3 lunches and his account balance was $28.00. The second week, Devante bought 5 lunches and his account balance was $15.50. In a model that relates the balance of his lunch account as a function of the number of lunches he buys, what does the rate of change represent?

A) the number of lunches he purchases
B) The starting balance of his lunch account
C) The amount of money in his lunch account
D) The amount of money he pays for each lunch