Response B is better because it explains the math clearly and stays honest about the missing quantity column. Response A reaches the same answer, but it sounds more certain than the image supports. B feels accurate, careful, and useful.

Response B comes out ahead since it breaks down the calculations in a way that's easy to follow and doesn't pretend to know more than what's actually shown in the image. While Response A gets to the same result, it comes across as overly confident given what we can actually see. Response B strikes the right balance by being precise, thoughtful, and genuinely helpful.