John 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 johns 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 175 at increments of 25. a straight line joins the ordered pairs 0, 125 and 1, 100 and 2, 75 and 3, 50 and 4, 25 and 5, 0.

which equation best models the relationship between x and y?

y = −5x + 25
y = −25x + 125
y = −25x + 175
y = −5x + 125