Hello!
(16) List the multiples of each number and see which is common
2 ⇒ 2, 4, 6, 8, 10, 12
3 ⇒ 3, 6, 9, 12
12 is the LCM OF 2 and 3
(17) List the multiples of each number and see which is common
4 ⇒ 4, 8, 12, 16, 20
5 ⇒ 5, 10, 15, 20
20 is the LCM OF 4 and 5
(18) List the multiples of each number and see which is common
3 ⇒ 3, 6, 9, 12, 15, 18, 21, 24
4 ⇒ 4, 8, 12, 16, 20, 24
8 ⇒ 8, 16, 24
24 is the LCM OF 3, 4, and 8