Calculation squares on a grids

There are 6 different types  of methods calculating the outside squares on a grids, I pick 2 type of ways to calculate the ouside  squares of the grid in a  10 by 10 grid
First method:
(4 x 10) - 4 = 36
      Or
(4n - 4) = 36 (in algebraic)


First i multplied the base and height then minus it with 4 because since  we cannot used the square 2 times, i subtrated it on every corner or edge of the square.
Here's some pictures;


Second Method:
10 + 8 + 10 + 8 = 36
           Or
n + (n - 2) + n + (n - 2) (in algebraic)

 First thing add the base and the height then subtract 2 on each left and right side because since the square  cannot be used 2 times so the left and the right will become 8.