Jeffrey will have no budget left after 19 days. This matches (D).
If you have trouble seeing this, you can use the answer choices to help you plug in. If (A) is true, the
budget at the start of the month, when days = 0, is $19. Plug these values into the equation to see if it is
true. Is 7 × 0 + 19 = 133? Not at all, so eliminate (A). If (B) is true, Jeffrey drinks a lot of coffee! Let’s try
some numbers and see if it works. For x = 1, the equation becomes 7(1) + y = 133 or y = 126, and for x =
2, it is 7(2) + y = 133 or y = 119. The difference in y, the budget remaining, is 126 – 119 = 7, so that’s not
$19 per day. Eliminate (B) so only (C) and (D) remain. These both have 19 for the number of days, and
the point (19, 0) would indicate that 19 is the x value, or days. If you saw that right away—great! That
would allow you to skip right to testing (C) and (D).
For (C), you can plug in 19 for days in the equation to get 7 × 19 + budget = 133, or budget = 0. Does that
tell you how many cups of coffee Jeffrey drank? You have no information about the cost of a single cup of
coffee, so the answer can’t be (C). It does tell you, however, that after 19 days, Jeffrey has no budget left,
so (D) is not only the one remaining answer, but it is also the correct one!