A model predicts that a company's monthly sales, in units, will be 50t + 200, where t is the number of months since launch. In month 4,…

A residual is the actual value minus the predicted value. The model predicts $50(4) + 200 = 400$ units for month 4. The actual sales were 410, so the residual is $410 - 400 = 10$, choice C. A positive residual means the model underestimated sales. Choice A (400) is the predicted value. Choice B (410) is the actual value. Choice D ($-10$) has the right size but the wrong sign, which comes from computing predicted minus actual. The question specifically says actual minus predicted.