Answer:
24 posts
Step-by-step explanation:
Length = 8 yards
So, No. of parts of 1 yards in 8 yards = 
So, One each length there will be 8 posts including 2 corners
So, Total posts on 2 lengths = 8+8=16
Width = 6 yards
So, No. of parts of 1 yards in 6 yards = 
Excluding 2 corners, There will be 4 lamps on each width
So, Total posts on both widths excluding corners = 4+4=8
So, Total posts on fence = 16+8 = 24
Hence He used 24 posts .