1, four cubes of the same size make up a cuboid, and six faces (the surface area of the cube) overlap, so you know that the surface area of the cube is (90/3 = 30.

) square centimeters.

2, just cut two knives, one horizontal and one vertical, and the side length is (

2) decimeter.

3. Two surfaces are added, and the surface area is increased (

2× 4× 4 = 32) square centimeters.