Freddy reads an equal number of pages of a book every week. The graph below shows the number of pages of the book left to read, y, after x weeks: A graph titled Freddy’s Book Reading shows Number of Weeks on the x-axis and Number of Pages Left on the y-axis. The scale on the x-axis shows numbers from 0 to 6 at increments of 1, and the scale on the y-axis shows numbers from 0 to 280 at increments of 40. A straight line joins the ordered pairs 0, 200 and 1, 160 and 2, 120 and 3, 80 and 4, 40 and 5, 0.

Which equation best models the relationship between x and y?
y = −5x + 40
y = −40x + 280
y = −40x + 200
y = −5x + 200