This requires some tricky manoeuvring. The key is to notice that you will end up with one wubba in each row, and if the third one is at (22,8), you can get the mirror to (22,9) with rotation but you can't continue south. So it has to be at (21,8).
Working backwards, the second wubba should be at
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×(21,7), because if it's at (22,7) then you need a south move facing SE to get the mirror to (22,10), which is impossible because the third wubba will block you
and the first wubba should be at
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×(22,6), because if all three are on the left, then again, the bottom wubba will block you when you try to move south.
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50th Skywatcher
