A cafeteria worker places a scoop of mashed potatoes on every tray. After 80 people had gone through the lunch line, there were 920 ounces of mashed potatoes remaining. After 120 people had gone through the lunch line, there were 800 ounces of mashed potatoes remaining. If p represents the number of people going through the lunch line and w represents the ounces of mashed potatoes remaining, which equation can be used to model this situation?