The side of the square is √(196 ft²) = 14 ft. The garden has 4 sides, so the total length of fence needed is ...
... 4 × 14 ft = 56 ft . . . . length of fence
If a post is placed every 7 feet, there will be 56/7 = 8 posts
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One post is needed at each of the 4 corners, and one is needed in the center of each of the 4 sides.