Draw fences between some of the posts so that each post is at the junction of exactly three fences.

These fences will divide the field into several paddocks; any paddock whose area is greater than a single triangle will contain a number, which will indicate the area of the paddock that contains it.

The boundary fence is already in place, so any post on the boundary only needs one more fence emerging from it in order to make up its full complement.

For example:

Here is the puzzle: