6. Suppose that R is a finite commutative ring with unity and let a E R with a 0. Define the map fa : R- R by fa(x)a (i) Show that if a is NOT a zero-divisor, then fa is one-to-one. (ii) Deduce from (i) and the fact that R is finite that a MUST be a unit in R. (ii) State the result that (i) and (ii) have just established.