There are two things to note in this question:
1) It can be easily identified that 2 and 3 are factors. Since the LCM of 2 and 3 is 6, it can be seen that any number which may be divided by 2 and 3 must also be divided by 6. Hence 6 is another factor.
2) For each of the multiples of 6, we can see that every other multiple is also a multiple of 4 i.e. 6,
12, 18,
24, 30,
36... Therefore, in this case, we must not overlook this fact here and the calculation of the sum becomes important to see whether 4 is also a multiple or not.
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