Based on the corporate valuation model, Wang Inc.'s total corporate value is $780 million. Its balance sheet shows $70 million notes payable, $140 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. $710 million

b. $570 million

c. $640 million

d. $620 million

e. $610 million