1) 21 = 3*7 и 18= 2*3*3 и НОК(18,21) = 2*3*3*7 = 126
2) 24 = 2*2*2*3 и 32 = 2*2*2*2*32 и НОК(24,32) = 96
3) 16 = 2*2*2*2 и 20= 2*2*5 и НОК(16,20) = 80
4) 20 = 2*2*5 и 35 = 5*7 и 75 = 3*5*5 и НОК(20,35,75) =2*2*3*5*5*7 = 2100.
5) 90 = 2*3*3*5 и 6=2*3 и 13 - простое. НОК(6,13,90)=2*3*3*5*13=1170.