july seventh what is the cost of a round trip ticket traveling first class on united airlines leaving from denver going to baltimore 
return flights ;return #1 that  are round trip ;return #2 that  are on  united airlines ;return #3 that  leave from  denver ;return #4 going to baltimore ;return #5 that  are first class ;return #6 that  are on  july seventh ;return cost of #7
['select', 'filter', 'filter', 'filter', 'filter', 'filter', 'filter', 'project']