For Part A, in creating the square, you did it correctly.
Now for Part B, you can create a right triangle by adding a point at -4, -3, and we'll call it, say, T.
Then you can use the Pythagorean's Theorem to find the length of one side of the square.
The Pythagorean's Theorem is

A would be the distance between P and T, and B would be the distance between Q and T. So then, a would be 7, and B would be 2.
To fill it in, it would be

or 49 + 4 =

or 53 =

or

= x
Which is equal to about 7.28
Now multiply that by 4 to get the perimeter, or 29.12
So the perimeter would be about 29.12