You have to have two different numbers to find common multiples
They are numbers which are not common multiples.
They are the common multiples of the two numbers.
There cannot be common multiples of a single number such as 345. Common multiples are multiples that two or more numbers have in common.
This cannot be determined because the common multiples of any two or more numbers are infinite.
A single number cannot have common multiples, common multiples can only be shared by two or more numbers.
All nonzero numbers have multiples. Any two numbers will have an infinite number of multiples in common. The smallest of these is known as the least common multiple, or LCM.
Those are known as "common multiples". The smallest POSITIVE of these common multiples is called the "least common multiple".
A common multiple is used to compare the multiples of two or more numbers - a single number cannot have any common multiples.
You need at least two numbers to compare multiples.
Since 3 and 5 are both prime numbers, the only common factor of the two numbers is 1. Perhaps you are thinking of common multiples, the first two common multiples of the two numbers are 15 and 30.