In order for the shape to be a rectangle the last vertex (lets call it D) must be the same vertical distance from C as A is from B (DC=AB), and the same horizontal distance from A as B is from C (AD=BC).
AB=DC=5
-3+5=2
BC=AD=9
-2+9=7
Therefore D is (7,2)
We already know the side lengths (5 and 9). Area is length by width. Therefore area = 5x9=45
