Based on this expression Surface area = (12)(6) + 1/2 (12)(8) + 1/2 (6)(9.5) we can deduce that the pyramid has a rectangular base of lenght 12 and witdh 6, since 12 and 6 are repeated in the other two expressions, whose expression seem to be the calculation of the are of a triangle. Since 8 and 9.5 are different and we don't have the picture of the pyramid, we can assume that 8 and 9.5 are the height of two different but adjacent faces. This implies that the tip of the pyramid is not in the middle of the rectangular base, so it has an irregular shape. Based on this facts, this means that we are missing the expression for the surface area of the remaining two faces.So the answer should be that the student added only three of the five faces, if the pyramid a non-regular shape.
In the case that the tip is in the middle of the base, the height is the same for the 4 triangular faces, so this would imply that the formula of the surface area is not applied correctly.
