What I did is first I look at the perfect square chart that we made then I saw that 225 is a perfect square then I saw that the square root is 15. Then so I made this.
6.) a.) The prime factorization of 64 is 2x2x2x2x2x2
b.) 64 is a perfect square because the first pair of numbers are the same.
11.) The square of 9 is 81 because if you multiply 9 and 9 the answer will be 81.
b.) the square of 11 is 121 because if you multiply 11 and 11 the answer will be 121.
15.) a.) 7
Here is a video if you want to understand it more.