A gardener has 26 feet of fencing for a garden. To find the width of the rectangular garden, the gardener uses the formula P = + 2 2,  w where
P is the perimeter,  is the length, and w is the width of the rectangle. The
gardener wants to fence a garden that is 8 feet long and plans on using all
of the available fencing. How wide is the garden? Solve the equation for w,
and justify each step.