Hello, jasonexher!
Draw a diagram to solve each exercise. . . . . Did you do that?
3. $\displaystyle P(1, 3)$ and $\displaystyle R(5, 5)$ are the endpoints of a diagonal of the rectangle $\displaystyle PQRS.$
Which sides of the rectangle are parallel to the xaxis? To the yaxis?
What is the perimeter of the rectangle? Code:
 Q R
 o        *(5,5)
 : :
 : :
 : :
 (1,3)*        o
 P S


 +    +        +   
 1 5
Can you guess where vertices $\displaystyle Q\text{ and }S$ are?
If you can do that, you can finish the problem . . .