How many years longer is the male and female national average combined over those rates for the county?
return males ;return females ;return national average in  years of #1 ;return national average in  years of #2 ;return county average in  years of #1 ;return county average in  years of #2 ;return sum of #3 and  #4 ;return sum of #5 and  #6 ;return the  difference of #7 and  #8
['select', 'select', 'project', 'project', 'project', 'project', 'arithmetic', 'arithmetic', 'arithmetic']