The difference of two sets, A - B, is defined as the set containing all elements of A except those in B. That is, A - B = A ( B'. Find A - B for each pair of sets in Problems 1-4 if U = {1, 2, 3, 4, 5, 6, 7, 8, 9}.

1. A = {1, 3, 7, 9} and B = {3, 5, 8, 9}

2. A = {1, 2, 3, 6, 9} and B = {1, 4, 5, 6, 7}

3. A = {2, 1, 5} and B = {1, 2, 3, 4, 5, 6}

4. A = {1, 2, 3, 4, 5} and B = {7, 8, 9}