For this, you can just count the boxes. First, not including the triangles on the side, the rectangle in the middle has an area for 2 because there are 2 boxes. The, each smaller triangle on the sides has an area of 1/2 because they each take up half a box. If we have 4 triangles, their total area is 2 (4*1/2 is 2). So when we add 2 with 2, we get a total area of 4.
Hope this helps!