Multiples of 9: 9, 18, 27, 36, 45, 54, 63, 72, 81, 90, 99, 108, 117, 126, 135, 144, 153, 162, 171, 180
Multiples of 12: 12, 24, 36, 48, 60, 72,84,96, 108, 120, 132, 144, 156, 168, 180
Multiples of 15: 15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 165, 180
The first number all 3 have in common is 180, which would be the LCM.