1 Check: Does the smaller number divide into the bigger one? If yes, the bigger number is the LCD! (e.g. 2 and 6 → LCD is 6).
2 If not: List the multiples of each until you find a match. (e.g. 4 and 6 → 4, 8, 12... vs 6, 12... Match at 12).
3 Shortcut: If they share no factors, just multiply them. (e.g. 3 and 5 → 15).