(Practice exam:3 Q4) a confusing question

Question 4 in the third pratice exam: why do we consider discounts metrics? metrics are created by our measures, but I don't understand what measures used to create discounts (Metrics), discount is just a number it isn't like the metric you gave in the video lesson (the average quarterly revenue per new customer is a result or the quotient of two measures) that is not the case here?