यदि {3,6,9,12,15,18,21}, B = {4,8,12,16,20}, C = {2,4,6,8,10,12,14,16}, D = {5,10,15,20}, तो निम्नलिखित को ज्ञात कीजिये
A - B

Answer

{3,6,9,15,18,21}