Common Solution:
P, Q, R, S, T, U, V, W, X and Y are placed one above the other in a stack, but not necessarily in the same order. At most, three boxes are placed below Q. Y is placed immediately below Q. So, three cases are possible i.e., Case 1, Case 2 and Case 3.
| Case 1: | Case 2: | Case 3: |
| | |
| | |
| | |
| | |
| | |
| | |
| Q | | |
| Y | Q | |
| Y | Q |
| | Y |
Two boxes are placed between Y and X. S is placed immediately above X. Four boxes are placed between S and R. P is placed immediately below R. So, Case 2 will be invalid.
| Case 1: | Case 3: |
| R |
| P |
| |
| S | |
| X | |
| S |
| Q | X |
| Y | |
| R | Q |
| P | Y |
T is placed immediately below V and immediately above W. Two boxes are placed between W and U. R is placed below Y. So, Case 3 will be invalid.
Finally, we get,
Four boxes are placed between X and P.
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