The person in charge of the exhibit shall give a detailed statement to the county board of all the person’s expenditures made to maintain the exhibit. The statement shall be given before November 2 of the year in which the exhibit is made. If the statement shows that any part of the appropriation is not spent, the balance shall be paid into the treasury of the county. When the county board approves the report, the person shall be relieved and discharged from all liability under the bond provided for in section 375.81.