Question

What is the perimeter?

Answer 1

The perimeter is the length of the outline of a shape. To find the perimeter of a rectangle or square you have to add the lengths of all the four sides. x is in this case the length of the rectangle while y is the width of the rectangle.
The perimeter, P, is:
P=x+x+y+y

P=2x+2y

P=2(x+y)

Answer 2

The perimeter is the length of the outside of an object. So for just one of those squares it would be 4. Or a 2x2 would be 8.

In this case you have 20 squares. Five of which two sides are exposed. All you need to do is count the outside lines

Your answer is 21ft.