Question 547747
since the corners of the sides share 1 post there will be 6 less posts than the combined total of 6*4=24 , 24-6=18 , so 18 posts are needed if you dont get this draw a hexagon put the 6 posts at the corners and draw 2 post in each side. so the 2 cornes of one side + the 2 posts inbetween is 4 posts a side.