Neeraj wants to add cubes to this stack to make the smallest possible solid cube. How many cubes must he add?

The stack is 3 cubes wide, 3 deep and 3 high, so the smallest cube is $3\times 3\times 3=27$. It already has $3+2+2+2+1+1+1+1=13$ cubes. He must add $27-13=14$. (13 is the number already there.)