Please help me with this math problem about width

Question

A garden is in the shape of a square with a perimeter of  feet. The garden is surrounded by two fences. One fence is around the perimeter of the garden, whereas the second fence is  feet from the first fence on the outside. If the material used to build the two fences is  per foot, what was the total cost of the fences?

Answer 1

56/4 = 14 feet for each side of the square

add 6 feet to get 20 feet by 20 feet for the outer fence

perimeter of the outer fence = 2(L+W) = 2(20+20) = 2(40) = 80 feet

total fences = 56 + 80 = 136 feet

at $1.29 per foot, total cost = 236(1.29) = $304.44