4 SOLVE AND SHOW ME STEP-BY-STEP SOLUTIONS, so I understand. Clearly explain the SOLUTIONS if they concern concepts. Humanize the answers to avoid sounding like those generated by AI.

4. The following table shows the demand for a product produced by a monopolist, who has a constant marginal cost and an average total cost of $45 per unit. Quantity (thousands of units) Price (dollars per unit) 0 120 1 105 2 90 3 75 60 5 45 6 30 a. Calculate total revenue and marginal revenue for level of quantity. b. What are the profit-maximizing output level and price level? In no more than three sentences, explain why. c. Calculate the monopolist's profit. d. Calculate the Lerner Index for this industry