Calculate squares on a grid

In Maths I learnt how to calculate the squares on a grid in different ways, there are 6 methods on how to calculate the outside squares on a grid and I will be showing you 2 of them. I learnt that the letters in maths are numbers and they are called algebra.

This is what I did to work out how many outside squares there are on a 10 by 10 grid using the first method:
I knew that there were ten squares on each four sides so all I had to do was simply add the tens on each sides all together then take away the 4 since the corners has doubled squares.

2nd method:
There are 10 squares on one side and I can't do tens again because it will double the squares on the corners so I will just add 2 nines on each sides. And then I will add ten on the last side, I will take away two because there are doubled squares on the corners so it will be '10+9+9+8=36' which is n+(n-1)+(n-1)+(n-2) = 36 in mathematical