How many volunteers were from Sofia, Tirnovo, and Pazardzhik combined?
return volunteers ;return #1 from  Sofia ;return #1 from  Tirnovo ;return #1 from  Pazardzhik ;return number of  #2 ;return number of  #3 ;return number of  #4 ;return sum of #5 and  #6 ;return sum of #7 and  #8
['select', 'filter', 'filter', 'filter', 'aggregate', 'aggregate', 'aggregate', 'arithmetic', 'arithmetic']