For the smart person to answer.

1.18, 42, 72, and 32 = 2

Step-by-step explanation:

For smaller numbers you can simply look at the factors or multiples for each number and find the greatest common multiple of them.

For 18, 42, 72, and 32 those factors look like this:

Factors for 18: 1, 2, 3, 6, 9, and 18

Factors for 42: 1, 2, 3, 6, 7, 14, 21, and 42

Factors for 72: 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, and 72

Factors for 32: 1, 2, 4, 8, 16, and 32