Calculating WACC. Find the WACC of William Tell Computers. The total book value of the firm’s equity is $10 million; book value per share is $20. The stock sells for a price of $30 per share, and the cost of equity is 15 percent. The firm’s bonds have a par value of $5 million and sell at a price of 110 percent of par. The yield to maturity on the bonds is 9 percent, and the firm’s tax rate is 40 percent.