Step by step explanation:
(a) How many cubes have only two faces painted?
As you can see in the diagram above, there are 4 on the front face, there will also be 4 on the back and another 4 missing that do not appear on those two faces (blue).
There are 12 cubes that have only 2 faces painted.
(b) What is the surface area of the painted cubes?
Each face of that cube has an edge of 9 cm, so the surface of each face must be:
[tex]A_1=9cm\cdot9cm=81cm^2[/tex]
And since the cube has 6 faces, the total must be:
[tex]\text{Area}=6\cdot81cm^2=486cm^2[/tex]
486 cm^2
