How many more household and housing units were there than families?
return households ;return housing units ;return families ;return number of  #1 ;return number of  #2 ;return number of  #3 ;return the  sum of #4 and  #5 ;return the  difference of #7 and  #6
['select', 'select', 'select', 'aggregate', 'aggregate', 'aggregate', 'arithmetic', 'arithmetic']