How many yards longer was Bullock's average yards of field goal than Gonzalez's average yards of field goals?
return field goals ;return #1 of Bullock ;return yards  of #2 ;return average of #3 ;return #1 of Gonzalez ;return yards  of #5 ;return average of #6 ;return difference of #4 and  #7
['select', 'filter', 'project', 'aggregate', 'filter', 'project', 'aggregate', 'arithmetic']