If the articles of incorporation or bylaws of a professional corporation do not provide a price or method of determining a price at which the corporation may purchase, redeem, or retire the shares, or that its shareholders may purchase the shares of a deceased shareholder or a shareholder no longer qualified to own shares in the corporation, then the price for the shares shall be the book value as of the end of the month preceding the death or disqualification of the shareholder. Book value shall be determined from the books and records of the corporation in accordance with the regular method of accounting used by the corporation.