To answer this question, you should know the algebraic expression :
x^2 + 2x + 1 = (x+1)^2
And area of the square is : side * side
So,
(x+1)^2 can also be written as (x+1)*(x+1) which can be seen as and square area with side (x+1)
So perimeter of square is 4 * side of a square
So answer will be
4* (x+1)
So,
4x +4 = answer or 4(x+1)