For most products, higher prices result in a decreased in demand while lower prices result in an increased in demand. Let D be the annual demand for a product in units and P be the unit selling price in dollars. The price-demand relationship can be described by the following linear function: D = 20,000 - 9P where P must be between $1,200 and $1,400. Show the mathematical expression for the total revenue, which is the annual demand multiplied by the unit selling price?