It is 40 because you have to find the area of each face so you would do 3*4 which equals 12 and since there is 4 of the triangles you do 12*4 which is 48 but when it's a triangle you have to cut it in half so it would really be 24.
Then for the square on the bottom you would do 4*4 which is 16 and then you would add the totals to get 40.
