Answer:
D
Step-by-step explanation:
The question states you need a square. That means whatever you do, must leave a square number like 49 or 64
If you add 6 or 7 to 56 you do not get 64 A and C are both wrong.
If you subtract 7 from 56 you get 49 which is a perfect square and all 4 sides will equal 7.
