On June 30, 2017, Walter Industries had outstanding $30 million of 6%, convertible bonds that mature on June 30, 2022. Interest is payable each year on June 30 and December 31. The bonds are convertible into 2 million shares of no par common stock. At June 30, 2017, the unamortized balance in the discount on bonds payable account was $4 million. On June 30, 2017, half the bonds were converted when Walter's common stock had a market price of $50 per share. When recording the conversion using the book value method, Walter should credit Common Stock at:

a. $10 million b. $12 million c. $11 million d. $13 million