a)A={172, 144, 30, 180, 120}
B={15, 30, 180, 120, 405}
C={27, 144, 15, 30, 180, 120, 81, 405}
b)A∩C={144, 30, 180, 120}
A∩B={30, 180, 120}
B∩C={15, 30, 180, 120, 405}
A∩B∩C={30, 180, 120}
A\B={172}
B\A={15, 405}
A\C={172}
C\A={27, 15, 81, 405}
B\C={15, 30}
C\B={27, 144, 81}