You misunderstood the input with the output, the input is "8" and the ouput is ["5", "7", "8", "9", "0"]

Thank you for your reply.

To work out the amount of boxes needed is the puzzle for this kata.

If I give the whole procedure of how to get the needed amount, it lost the point.

The example is just intended to show the procedure of how boxes moving work, then from there one can work on the amount for it.