Look at it like 2 shapes a rectangle and a triangle.
Area of the rectangle = W * L
Area of the rectangle = 3* 8
Area of the rectangle = 24 ft²
Area of a triangle = 1/2 bh
Area of a triangle = 1/2(7)(4)
Area of a triangle = 1/2 (28)
Area of a triangle = 14 ft²
Then add both areas= 24 + 14= 38 ft²