Based on the corporate valuation model, Carton Inc.'s value of operations is $500 million. Its balance sheet shows: $75 million of short-term investments that are unrelated to operations $100 million of accounts payable $150 million of notes payable $100 million of long-term debt $40 million of common stock (par plus paid-in-capital) $160 million of retained earnings. What is the best estimate for the firm's value of equity, in millions