ANSWER
(0,s)
EXPLANATION
The coordinates of vertex A of rectangle ABCD is A(0,0) and that of C(r,s).
When we name the rectangle in anticlockwise direction, then B will have coordinates (0,s).
The reason is that, the x-coordinate of B will be the same as the x-coordinate of A, because they are on the same vertical line.
The y-coordinate of B is the same as the y-coordinate of C because they are on the same horizontal line.
