Area has two dimensions: the length and the width. It is measured in square units such as square feet, square meters or square inches. To solve for the area of a rectangle, multiply the length by the width, with the formula: A = L * W where A is the area, L is the length, W is the width. Given 5 feet for the length and x feet for the width, substitute the given to the formula to come up with an equation A=5x.