|A) 17||B) 18|
|C) `19||D) 20|
The fence will consist of one more post than there are chains. (e.g. P-c-P-c-P).
Therefore, a total length has to be a multiple of the length of the chain plus one post (5.5) plus one post extra.We have length = (5.5n + 0.5), where n can be any positive whole number. If n= 3, length =17