Query: According to the 2000 United States Census, how many housing units were there in Atlantic City?
Context: The population density was 3,569.8 people per square mile (1,378.3/km2). There were 20,219 housing units at an average density of 1,781.4 per square mile (687.8/km2). The racial makeup of the city was 44.16% black or African American, 26.68% White, 0.48% Native American, 10.40% Asian, 0.06% Pacific Islander, 13.76% other races, and 4.47% from two or more races.