area of inside (small) rectangle = 6x
area of outside (large) rectangle = (x+3)(3x-2)
the area of shaded region : (x+3)(3x-2) - 6x = 24
solve for x
(x+3)(3x-2) - 6x = 24
3x^2 +9x -2x - 6 -6x = 24
3x^2 +x - 6 = 24
3x^2 +x - 6 - 24 =0
3x^2 +x - 30 = 0
(3x-10)(x+3)= 0
3x-10 = 0
3x = 10
x = 10/3
x+3 = 0
x = -3
