Question 39810
Let the width be w.  The length is then 2w - 6.  Multiply them to get the area.
A = LW
A = (2w - 6)w
108 = w(2w - 6)
2w^2 - 6w - 108 = 0
w^2 - 3w - 54 = 0
(w - 9)(w + 6) = 0
w = 9 or w = -6 (impossible) so
w = 9 and 
length = 2(9) - 6 = 12