The perimeter of a rectangular garden is 72 feet. it's length is 3 times it's width. find the length and width of the garden

Length is 27 feet and Width is 9 feet.

Given:
Perimeter = 72 feet
Length = 3w
Width = w

Perimeter = 2 (length + Width)
72 feet = 2 (3w + w)
72 feet = 2 (4w)
72 feet = 8w
72 feet / 8 = w
9 feet = w  

width = 9 feet
length = 3w = 3*9 = 27 feet

Aand b are correctly balanced reactions. they have the same number of atoms in both sides of the reaction