Multiples of seven include 7, 14, 21, 28, 35, 42, 49 and so on. For them to be common, they need to be compared to another set of multiples.
84
693, 924.
Any multiple of 21.
28, 280, 2800
7 is a prime number. The answer is 1.
154 (there is only one least common multiple)
They are all multiples.
14, 28, 42
The LCM is 56.
28, 56, 84, 112, 140.
There are no multiples of seven because seven is a prime number
Those are known as "common multiples". The smallest POSITIVE of these common multiples is called the "least common multiple".