The university — as an agency or instrumentality of the State of Iowa as provided by Iowa Code 423.3(31) —  is exempt from paying Iowa sales tax on purchases used for public purposes. The university is exempt from collecting Iowa sales tax on sales to its customers located in Iowa where the entire profits from those sales are expended for educational or charitable purposes as provided by Iowa Code 423.3(78) and Iowa Administrative Code [701]17.1(6). This exemption does not apply to ticket sales for athletic events, which are specifically taxable by the Iowa Code regardless of how the proceeds are expended.