How difficult is it in reality to compute the corporation’s marginal tax rate? Why? What are the factors that are really important? If we observe that a firm has net operating losses, does this mean...

How difficult is it in reality to compute the corporation’s marginal tax rate? Why? What are the factors that are really important? If we observe that a firm has net operating losses, does this mean that the firm has not hired a very smart tax-planning strategist?