The answer is identity property of addition.
Answer:
A: if you cut it parrallel to the base, it will take the shape of the base, and the base is a rectangle, so it will still be a rectangle.
B: if you cut it perpendicular to the base, it will take the shape of the side face, making it a square
The side corresponding to AC is ~
2 5/12 because it is an improper fraction