Task: Question Decomposition
Input (English): question: what's the cheapest round trip fare between boston and washington 
Output (English): #1 return flights 
#2 return #1 that  are round trip 
#3 return #2 between boston 
#4 return #3 and washington 
#5 return fares of #4 
#6 return #5 that  is  the  cheapest