For the following, verify that the subset D of the group G is a difference set and determine the value of A. (a) D={0,1,2,4,5,8, 10) and G=Z15 (b) D={(0, 1), (0, 2), (0,3), (1, 0), (2, 0), (3,0)} and G=Z4 x Z4. Recall that Z4 x Z4 is the group whose elements are ordered pairs of elements of Za with the operation being + componentwise..