If the question is 400 divide by 3/16 then:
400 divide by 3/16 = 400 times by 16/3 = (400*16)/3 = 6400/3 = 2133 1/3
If the question is "400 people were surveyed, 3/16 of them supported the tax hike, how many supported the tax hike?" then:
400 times 3/16 = (400*3)/16 = 1200/16 = 75