The surface area of a cube is the combined area of all of its faces. The faces of a cube are squares, so to find the area of one face, we simply need to multiply the side length, which is 20, by itself.
20 * 20 = 400
So one face has an area of 400 units squared. To find the surface area, we just need to add all of the individual areas together. Cubes have 6 faces, so we can just multiply 400 by the amount of faces there are.
400 * 6 = 2400
The net, when folded into a cube, has a surface area of 2,400 units squared.
Hope that helped! =)
