Aaron has a budget of $100 per month to spend on lunch. He made a table showing the total amount of lunch money he will have left after the given number of lunches.

Number of lunches 0 5 10 15
Total amount of lunch money left ($) 100 75 50 25
Which equation, in standard form, represents the relationship between the number of lunches, x, and the amount of lunch money Aaron will have left, y?

x + 5y = 100

100x + y = 5

x + 100y = 5

5x + y = 100