D.C. Code § 29-515
If the articles of incorporation, bylaws, or an agreement among the shareholders, does not fix the price at which the corporation or its shareholders may purchase the shares of a disqualified, deceased, legally incompetent, retired, or expelled shareholder, or does not provide a method of determining such price, the price for such shares shall be the book value of the shares on the last day of the month immediately preceding the disqualification, death, adjudication of incompetence, retirement, or expulsion of the shareholder, determined under generally accepted accounting methods, consistent with the method of accounting used by the corporation for federal income tax purposes, by an independent certified public accountant employed by the corporation for the purpose.
D.C. Code § 29-515