In the given figure, there are two right angled triangles.
Area of triangle = 1/2 × b × h
Area of shaded region = area of larger triangle - area of smaller triangle
= 1/2 × 15 × 18 - 1/2 × 8 × 9
= 135 - 36
= 99 ft^2
Thus, area of shaded region is 99 ft^2.