Based on the corporate valuation model, Wang Inc.'s total corporate value is $750 million. Its balance sheet shows $100 million notes payable, $200 million of long-term debt, $40 million of common stock (par plus paid-in-capital), and $160 million of retained earnings. What is the best estimate for the firm's value of equity (in millions)?

a. $450

b. $531

c. $360

d. $423

e. $522