If you make a multiplication table for the given ring, you can see that 6*x = x for all x in R, so 6 is the unity.
Is the x just the ring in the problem?
--Jrendall 20:26, 10 March 2009 (UTC)
x would be each element in the ring, and when you multiply each element by 6, you see that in modulo 10, you end up with the element that you started with.
