How do you find the perimeter of a dented square here is the

To find the perimeter of anything, you look at it and figure out how far
an ant has to walk if you put it down at one corner, and it walks all the way
around all the edges until it gets back to where it started.

On this square with a bite cut out of it, I see three x's and three 1's that
the ant has to walk.  That looks a lot like   3x+3  to me.