We have the measurements of a length of 4, and width of 2. The area of a rectangle is Length times Width, therefore: 4x2=8 ft squared for the rectangle.
Now the Triangle: We see that the whole left side is 4ft, and that the rectangle's width is 2ft; therefore, the left side of the triangle is 2 ft (4-2). The area of a triangle is 1/2Base times Height. The base is 4, and the height is 2; therefore: 1/2x4x2=4 ft squared.