The purchase price paid or charged on direct sales to and direct purchases by a public school operating as an educational institution having a curriculum comparable to a grade, grammar, junior high, high school or college, requiring daily attendance and enrollment of forty (40) or more students in the conduct of its educational functions and activities are exempt, provided that a letter of exemption from the City is possessed by the school. Schools held or conducted for private or corporate profit do not qualify for exemption. (1968 Code §3-75; Ord. 79-179; Ord. 01-42; Ord. 24-30)