a) 6 = 2 * 3
12 = 2*2*3 cmmdc 2*3=6 cmmmc 2*2*3 =12
b) 6 = 2 * 3
12 = 2*2*3
18 =2*3*3 cmmdc 2*3=6 cmmmc 2*2*3*3 =36
c) 30 = 2 * 3 *5
40 = 2*2*2*5
50 =2*5*5 cmmdc 2*5=10 cmmmc 2*2*2*3*5*5 =600
b) 63 = 3*3*7
72 = 3*3*2*2*2
81 =3*3*3*3 cmmdc 3*3=9 cmmmc 2*2*2*3*3*3*3*7 =4536