Given
The area of the shaded region is 36 ft2 .
Answer
Area of rectangle = 36
l x b = 36
12 x b = 36
b = 36/12
b = 3
shaded region is a triangle with area = 1/2 x base x height = 1/2 x 3 x 12 = 12 ft2
Area of unshaded region = 36 - 18 = 18ft2
Option B is answer.