A great way to divide fractions is to use the "leave it, change it, flip it" method. You leave the first fraction as it is, change the division sign to a multiplication sign, and flip the second fraction so you get the reciprocal. Like this:
-5/7 ÷ 6/7
-5/7 x 6/7
-5/7 x 7/6
Then you multiply through. First -5 x 7, -35, and then 7 x 6, 42, to get -35/42. Because both of these are divisible by 7, we can simplify to get -5/6.
The area of a square is its side length squared. So the side length of the square squared is 42, so the side length of the square is sqrt(42). The perimeter of the square is 4 times the side length, or 4sqrt(42), which is approximately 25.92.