It just depends but usually it is an inverse for the original equation that you were given
11 squared is 121
20 squared is 400
121+400= 521
The approximate square root of 521 is approximately 22.8254
As you can see in the picture above, there are six faces of a rectangular prism; two are formed with dimensions width and height, two are formed by the dimensions length and width, and two are formed by the dimensions length and height. So, if you know the length, width, and height of the rectangular prism, then the formula for the surface area is
=(2⋅ℎ⋅ℎ)+(2⋅ℎ⋅ℎℎ)+(2⋅ℎ⋅ℎℎ)