Bob must choose a number between 61 and 107 that is a multiple of 3, 5, and 6. If there are more than one number, separate them with commas.

Multiples of 3 between 61 and 107 are

63, 66, 69, 72, 75, 78, 81, 84, 87, 90, 93, 96, 99, 102, 105

multiples of 5 between 61 and 107 are

67, 70, 75, 80, 85, 90, 95, 100, 105

multiples of 6 between 61 and 107 are

66, 72, 78, 84, 90, 96, 102

With the 3 and the 5 they share the numbers,

75, 90, 105

The 3 and 6 share the numbers

66, 72, 78, 84, 90, 96, 102

The 5 and 6 share the number

90

The only one I see that's common with all three of them is

90