Arm hires labor in a perfectly competitive labor market. lts current prot-maximizing hourly output is 100 units, which the rm sells at a price of $10 per unit. The marginal physical product of the last unit of labor employed is 5 units per hour. The rm pays each worker an hourly wage of $20. a. What marginal revenue does the rm earn from sale of the output produced by the last worker employed? $ . (Entera numeric response using an integer.)