Let f(x) = + 1 Za[r] and let R = Za[r]/I, where I = (f(x)). (a) Show that R is a field with 9 elements. (b) Denote by 0 = 0+1, 1 = 1 + 1, and a :=z+I. Write the other 6 elements of R in terms of a and determine the multiplicative inverse of each nonzero element. (e) Prove that RZ[i].