This can be separated into 2 different shapes.
The top portion is a rectangle 3 feet wide by 3 feet high and the lower portion is a square 3 feet wide by 3 feet high.
Area of top = 3 x 2 = 6 square feet.
Area of bottom = 3 x 3 = 9 square feet.
Total area = 6 + 9 = 15 square feet.