140 = 2 * 2 * 5 * 7
204 = 2 * 3 * 67
It's like we're making a parts list that can be used to make either number (140, 204). In this case our parts list is 2 * 2 * 3 * 5 * 7 * 67 because that's the list that has enough parts to make either 140 or 204.
2 * 2 * 3 * 5 * 7 * 67 = 28140
Answer: The least common denominator (LCD) is 28140.