Jenny made a block using small cubes, each having a volume of 9 cubic cm. To…

Jenny made a block using small cubes, each having a volume of 9 cubic cm. To make the block, she used 4 small cubes along the length, 8 small cubes along the width, and 16 small cubes along the depth. She realised she had used more small cubes than necessary — the block would look exactly the same from outside even if it were hollow, with only the outer shell of cubes present. What is the minimum number of cubes she needs to take out so that the block becomes hollow?