Answer:
(5,6) and (8,3)
Explanation:
A and C are two of the corners of the square.
Imagine the top LEFT corner. If you drew a line straight UP from A and to the LEFT of C, it would meet at (5,6).
Now picture the bottom RIGHT corner. If you drew a line from A to the RIGHT and then another line from C DOWN, those lines would meet at (8,3).
I drew a pic showing the square you are trying to create! See attached.