question: What is the maximum miles per gallon of the car with 8 cylinders or produced before 1980?
#1 return cars 
#2 return #1 with  8 cylinders 
#3 return #1 produced before 1980 
#4 return #2 ,  #3 
#5 return miles per gallon of #4 
#6 return the  maximum of #5