question: which is the flight number for the us air flight from philadelphia to boston is it 279 or is it 137338 
#1 return flights 
#2 return us air of #1 
#3 return #2 from  philadelphia 
#4 return #3 to boston 
#5 return flight number of #4 
#6 return which  of 279 or  137338 is  #5