A square garden is 12 feet long on each side. Janet needs to put a post on each corner. She also needs to put a post every 3 feet on each side. How many posts does Janet need?

There should be 12 posts. If the garden is square and each side is 12 feet and you have one post at each corner you start with four. From there every three feet you add a post so you put 2 more posts between every corner post which when counted add up to 12 posts.