question: What is the average number of working horses of farms with more than 5000 total number of horses?
#1 return farms 
#2 return horses on  #1 
#3 return number of  #2 for each  #1 
#4 return #1 where #3 is  higher than 5000 
#5 return horses on  #4 
#6 return #5 that  are  working 
#7 return number of  #6 
#8 return average of  #7