Please solve and explain your steps as i want to know the steps and not just the answer

28. Supply and demand for economics textbooks at UTM are given by D = 2500 - 10P and S = 10P -500. A wealthy old man from Oakville once took economics at UTM. He would like to help the students who are currently in ECO100 and offers to provide a per-unit subsidy to the bookstore. His goal is to reduce the price paid by students to $100. a. Provide a Supply and Demand diagram that illustrates and quantifies how the equilibrium price would be affected by this subsidy. b. He's ready to pay. How big a cheque will he need to write