Let A = {3, 6, 12, 15, 18, 21}, B = {4, 8, 12, 16, 20}, C = {2, 4, 6, 8, 10, 12, 14, 16} and D = {5, 10, 15, 20}. Find
(i)     A – B
(ii)    A – C
(iii)   A – D
(iv)   B – A
(v)    C – A
(vi)   D – A
(vii)  B – C
(viii) B – D
(ix)   C – B
(x)    D – B
(xi)   C – D
(xii)  D – C

A = {3, 6, 12, 15, 18, 21},
B = {4, 8, 12, 16, 20},
C = {2, 4, 6, 8, 10, 12, 14, 16} 
and D = {5, 10, 15, 20}.
(i) A – B = {3, 6, 15, 18, 21}
(ii) A – C = {3, 15, 18, 21}
(iii) A – D = {3, 6, 12, 18, 21}
(iv) B – A = {4, 8, 16, 20}
(v) C – A = {2, 4, 8, 10, 14, 16}
(vi) D – A = {5, 10, 20}
(vii) B – C = {20}
(viii) B – D = {4, 8, 12, 16}
(ix) C – B = {2, 6, 10, 14}
(x) D – B = {5, 10, 15}
(xi) C – D = {2, 4, 6, 8, 12, 14, 16}
(xii) D – C = {5, 15, 20}