question: list departure times from denver to philadelphia which are later than 10 o'clock and earlier than 2pm 
#1 return flights 
#2 return #1 from denver 
#3 return #2 to  philadelphia 
#4 return #3 later than  10 o'clock 
#5 return #4 earlier than  2pm 
#6 return the  departure time of #5