question: How many years is the age range for estimated average requirements for women taking 18.0 mg/day?
#1 return the  estimated average requirements for women taking 18.0 mg/day 
#2 return the  age range in  years of #1 
#3 return the  highest of #2 
#4 return the  lowest of #2 
#5 return the  difference of #3 and  #4