How many months after Engelbrekt summoned representatives from the four Estates to a Diet in Arboga was he assassinated?
return Engelbrekt summoned representatives from  the  four Estates to a Diet in  Arboga ;return Engelbrekt was  assassinated ;return month of #1 ;return month of #2 ;return the  difference of #4 and  #3
['select', 'select', 'project', 'project', 'arithmetic']