So if you take the area under that rate curve, that's going to give you the net change in revenue from month one to month five, how much that increased. So if you add that to the amount that she made in month one, well that tells you the total she makes from essentially time zero all the way to month five. And they're saying that is equal to 19. So let's see which of these choices are consistent with that. Julia made an additional $19,000 between months one and five. Choice A would be correct if you didn't see this three over here, because just the definite integral is the additional between months one and five, but that's not what this expression says. It says three plus this is equal to 19.