The top view of the cube in the above picture, red is the top view of the sphere, and gray is the limit position of the sphere. Because the contact surface between the ball and the cube is a small point, and the surface of the cube is tangent to the surface of the ball, the green square in the picture is the area where the ball and the cube can contact. The side length of the green square is 2 mm, so the dough maker is 4 square decimeters.

Because the cube has six identical faces, the surface area of the box that can contact the ball is 24 square decimeters.

The box has six sides, and the inner surface is 96 square decimeters, so the area where the inner surface of the box can't touch the ball is (96-24)=72 square decimeters.

I don't know if I made it clear. Ask me if you don't understand. I hope it can be adopted. Thank you ~ ~ ~