A solid cube of 4 inches has been painted red, green and black on pair of opposite faces. It has been cut into one inch cubes. How many cubes have only Red and Green faces?

On the basis of given all information in above question , we get
There are 4 + 4 = 8 cubes in layer ?1 and 4 + 4 = 8 cubes in Layer ? 4 which have one face painted green and one face painted red.
Thus there are 16 such cubes.