It is called a difference of squares because there are two things squared being subtracted. You can recognize it when there are two terms, subtraction between the two of them, and you know the square root of both
The probability is 6/9 or 66.6%
Ok, so I worked out the problem.
So for part a) you just multiply 8 by 25% then add the product to get the new perimeter.
Part B you Add all sides for the original square and the new square to get the perimeters of each then you divide the old square perimeter by the new square perimeter to get the percentage.
Part C you get the areas pf bother squares then divide the old square area by the new square area to get the percentage change.
If you have any questions, let me know.