I just did my usual mess with it til I solve it. But I found what I think is a WT help on the slider puzzle...
SPOLIER BELOW
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START ORDER
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| 5| 8| 4|14| | 1| 2| 3| 4|
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| 9| 6|12| 3| | 5| 6| 7| 8|
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|10| 2|13| 1| | 9|10|11|12|
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|11| 7|15| X| |13|14|15| X|
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- Always try to arrange (in this order)
1. the four pieces on the left (1,5,9,13),
2. then the rectangle up right (2,3,4,6,7,8)
3. then the remaining five (10,11,12,14,15).
You can arrange every step without modifying pieces from preceding steps!
That makes it totally easy!
Hope this helps
Laura