Based on the corporate valuation model, Wang Inc.'s total corporate value is $840 million. Its balance sheet shows $60 million notes payable, $120 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. $780 million

b. $660 million

c. $720 million

d. $680 million

e. $700 million