Seven boxes- B1, B2, B3, B4, B5, B6 and B7 are kept one above the other but not necessarily in the same order. The bottommost position is numbered as 1, above that 2 and so on.
Four boxes are kept between box B2 and box B6.
Box B2 is kept above box B6.
|  | Case 1 | Case 2 | 
| Position | Box | Box | 
| 7 | B2 |  | 
| 6 |  | B2 | 
| 5 |  |  | 
| 4 |  |  | 
| 3 |  |  | 
| 2 | B6 |  | 
| 1 |  | B6 | 
The number of boxes kept above box B2 is same as the number of boxes kept below box B4.
Box B4 is not kept at the bottommost position.
Thus, Case 1 gets cancelled.
|  | Case 2 | 
| Position | Box | 
| 7 |  | 
| 6 | B2 | 
| 5 |  | 
| 4 |  | 
| 3 |  | 
| 2 | B4 | 
| 1 | B6 | 
Two boxes are kept between box B1 and box B5.
Box B7 is kept immediately below box B1.
| Position | Box | 
| 7 | B5 | 
| 6 | B2 | 
| 5 |  | 
| 4 | B1 | 
| 3 | B7 | 
| 2 | B4 | 
| 1 | B6 | 
Now, box B3 is remaining.
| Position | Box | 
| 7 | B5 | 
| 6 | B2 | 
| 5 | B3 | 
| 4 | B1 | 
| 3 | B7 | 
| 2 | B4 | 
| 1 | B6 | 
This is the final arrangement.
Box B3 is kept immediately above box B1 and immediately below box B2.