Question 883554
That depends.  Are you looking for each person to contribute an equal amount?  That doesn't seem quite fair since A's boots are more expensive.  Is there more information?
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In a real-life situation, boots A would be charged and B & C would be free (always the higher priced item is charged).  In that case, they should split it equally, $133.33 each.
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If, however, you're looking for them to pay based on the value of their boots, we still need to know WHICH boots are free.  Again, assuming that A pays and B&C are free:
The total value of the boots are 400+350+219 (only C pays sales tax???) = 969
Take the value of each and divide by the total value to see each person's share.
A: 400/969 = 41.3% (rounded)
B: 350/969 = 36.1%
C: 219/969 = 22.6%