Question 39808
Let the width be w.  The length is then w+8.  We multiply them to get area.
A = LW
A = (w+8)w
105 = w(w+8)
w^2 + 8w - 105 = 0
(w + 15)(w - 7) = 0
w = -15 (impossible) or
w = 7 inches