Can you please explain in details with graphs if possible the concept of monopolist, MC and MRHow can I read such a graph and how did we come up to this answer

22) A monopolist faces the demand curve shown below, and incurs a cost of $20 for each unit it sells. What will be the price and quantity sold? $90 $80 $70 $60 PRICE $50 $40 $30 $20 MC $10 MR DEMAND CURVE 10 15 20 25 30 35 40 45 QUANTITY The price will be $20 and the quantity sold will be 15 At a quantity of 15, the monopolist could charge $50 per unit. The price will be $50 and the quantity sold will be 15 correct Marginal cost = marginal revenue at a quantity of 15. The monopolist will sell 15 cars, and determine price based on the demand curve. The price will be $40 and the quantity sold will be 20 The monopolist will sell the quantity of cars where marginal revenue = marginal cost. The price will be $20 and the quantity sold will be 30 The monopolist will sell the quantity of cars where marginal revenue = marginal cost