Part A is where you list a few cases but not necessarily all possible scenarios. Part B is where you actually try to list every single case.
The way you have done part A, you have found every possible scenario. There are no other ways to arrange the blocks uniquely. There are only four distinct configurations. So the answer to part B is 4. There are no other ways (other than what you've listed) to multiply three whole numbers to get 20.
So in a sense, there's not much else to do but count the number of cases you've written for part A. By the way, nice work on listing all of the cases.
