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
Any multiple of 21.
693, 924.
28, 280, 2800
They are all multiples.
7 is a prime number. The answer is 1.
154 (there is only one least common multiple)
14, 28, 42
The LCM is 56.
28, 56, 84, 112, 140.
Those are known as "common multiples". The smallest POSITIVE of these common multiples is called the "least common multiple".
There are no multiples of seven because seven is a prime number