Question 1143477
<pre>
It's the same as the number of distinguishable arrangement of the row of 6
letters BBRRWW. 

That's because For any distinguishable arrangement of those 6 letters, we 
can always put the left shoe of each color left of the right one of the same
color.  

Since there are 6 letters, the 2 B's are indistinguishable, the 2 R's are
indistinguishable and the 2 W's are indistinguishable.   

So the answer is {{{6!/(2!2!2!)=720/(2*2*2)=720/8 = 90}}} 

Edwin</pre>