A parallelepiped of the dimensions you give is not a cube. A cube has 6 square faces.

The area of your right parallelepiped will be twice the sum of the following

(2 ft)*(6 ft), (2 ft)*(8 ft), and (6 ft)*(8 ft).

Each face of a given size has a matching one of the same size on the opposite side of the object.

total area = 2(12 ft

The area of your right parallelepiped will be twice the sum of the following

(2 ft)*(6 ft), (2 ft)*(8 ft), and (6 ft)*(8 ft).

Each face of a given size has a matching one of the same size on the opposite side of the object.

total area = 2(12 ft

^{2}+ 16 ft^{2}+ 48 ft^{2}) = 2(76 ft^{2}) = 152 ft^{2}.