Tom wants to fence in his yard to keep his dog from running out into the street. He knows how many square feet his yard is, but he needs to know the perimeter. The area of Tom's back yard is 400 feet squared. Tom's yard is in the shape of a square. How many feet of fencing does Tom need to buy?

80 ft

Step-by-step explanation:

1.) Since his yard is a square, the area is side^2, so take √400 to get the one side (20 ft)

2.) Then take that 20 ft and multiply it by four (or add it four times if you really wanna do that) because perimeter, which is what you need to find to get the length of fencing, is all four sides added

3.) 20*4 = 80 so it's 80 ft