The correct answer is Hawaii, as it was not acquired as a result of the Spanish-American War. In fact, Hawaii was annexed by the United States in 1898 with the Newlands Resolution, as an organized incorporated territory. It received statehood in 1959.
Guam, Philippines and Puerto Rico, on the other hand, were ceded by Spain to the United States for 20 million dollars as a result of its defeat in the war.