Factors: 1, 2, 3, 6, 7, 14, 21, 42 Multiples: 42, 84, 126 and so on.
The factors of 7 are 1 and 7. Neither of them are multiples of 42. Put the other way, 7, 14, 21 and 42 are multiples of 7 that are factors of 42.
35, 42, 49
Factors: 1, 3, 7, 21 Multiples: 21, 42, 63, 84 and so on.
Multiples don't add. Addends add, like 13 + 14 + 15 = 42 but I suspect you want factors, specifically prime factors. 2 x 3 x 7 = 42
1, 2, 3, 6, 7, 14, 21, 42 42, 84, 126 and so on
1344 is a multiple of 42. 42 is a factor of 1344. Factors go into numbers, numbers go into multiples.
Factors of 21 = 1, 3, 7, 21 Multiples of 21: 21, 42, 63, 84, 105, 126, 147 +21 . . .
Factors of 126 are 1, 2, 3, 6, 7, 18, 21, 42, 63, 126 Of those factors, 3, 6, 18, 21, 42, 63, 126 are multiples of 3.
They are 42 and 48.
Factors: 1, 3, 7, 21. Multiples: 21, 42, 63, 84, 105, 126, 147, 168, 189, 210 +21 . . .
21, 42, 63 and so on.