question: How many more days did the population grow until 1970 than the 1860?
#1 return the  population 
#2 return days that #1 grow 
#3 return #2 until 1970 
#4 return #2 until 1860 
#5 return number of  #3 
#6 return number of  #4 
#7 return difference of #5 and  #6