Hello!
The answer is:
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Why?
A multiple of a number is the repeated sum of itself, for example:
Multiple of the number 1 are: 1, 2, 3, 4, 5 and so...
Multiple of the number 3 are: 3, 6, 9, 12, 15 and so...
From the example we have:
Multiple of the number 3 are: Itself, (3+3), (3+3+3), (3+3+3+3), (3+3+3+3+3) and so...
So,
Multiple of
are:

Have a nice day!