Upon the delivery of the biennial report required under section 21-304 to the Secretary of State, it shall be the duty of every foreign corporation doing business in this state to pay to the Secretary of State an occupation tax each even-numbered calendar year beginning January 1 and become due and assessable on March 1 of that year and become delinquent if not paid by April 15 of each even-numbered year. The occupation tax shall be measured by the property employed by the foreign corporation in the conduct of its business in this state. For such purpose the property shall consist of the sum total of the actual value of all real estate and personal property employed in this state by such foreign corporation in the transaction of its business. The occupation tax to be paid by such foreign corporation shall be based upon the sum so determined and shall be considered the capital stock of such foreign corporation in this state for the purpose of the occupation tax. The schedule of payment shall be double the occupation tax set forth in section 21-303, or any amendments thereto, except that the occupation tax shall not exceed thirty thousand dollars, and the Secretary of State, or any person deputized by the Secretary of State, shall have authority to investigate and obtain information from such corporation or any state, county, or city official. Such officers are authorized by this section to furnish such information to the Secretary of State, or anyone deputized by the Secretary of State, in order to determine all facts and give effect to the collection of the occupation tax.