The edges in these 4 graphs show the colour pairings of opposite faces of the 
cubes.<br><br>
To solve the problem combine all 4 graphs then look for 2 subgraphs, one representing 
the colours 
on the front and back walls of the tower and the other representing the colours 
on the left and right hand 
walls of the tower, such that each contains all 4 colours and precisely one edge 
of each numbered cube.<br>
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<img src="mcprob4/clue2.gif" alt="Clue for Instant Insanity" width="577" height="145">