(a) The fiscal year of an authority is a calendar year, unless it is changed by the board.
(b) An authority shall keep a complete system of accounts. An independent certified public accountant or a firm of independent certified public accountants shall prepare an audit of an authority's affairs each year. A signed copy of the audit report shall be delivered to each member of the board within 120 days after the last day of the fiscal year. A copy of the audit shall be kept on file at the authority office and, as a public record, is open for inspection by any interested person during normal office hours.