If you dig a hole in a cube with a side length of 10 cm on the surface of a cube with a side length of 20 cm, how much has the surface area of a large cube increased?

If you dig a hole in a cube with a side length of 10 cm on the surface of a cube with a side length of 20 cm, how much has the surface area of a large cube increased?

There are four more 10 * 20 rectangular faces in the cuboid hole, but two less 10 * 10 square faces
So the surface area increases by 20 * 10 * 4-10 * 10 * 2 = 600 square centimeters