question: How many months passed between Erard taking up position in Noyers and the Blanche of Navarre besieging it?
#1 return Erard taking up position in  Noyers 
#2 return the  Blanche of Navarre besieging Noyers 
#3 return when  was  #1 
#4 return when  was  #2 
#5 return difference of #4 and  #3 in  months