If a number is comprised of multiples of x, then it, itself, is a multiple of x. Is it true/provable and there a name for this principle? [duplicate]

Take an integer, say 6.

Then make a number that is a combination of multiples of 6. Example:

36 72 18 12 24 72 90

The assertion is 36,721,812,247,290 is divisible by 6. And indeed it is (quotient: 6,120,302,041,215).

I haven't been able to disprove this with trial and error. Every number I use works.

Using 236 as base and 1,180 | 944 | 4,720 as multiples of 236, you get:

11,809,444,720 / 236 = 50,040,020
94,411,804,720 / 236 = 400,050,020
47,209,441,180 / 236 = 200,040,005

Is this expressing some trivial math property (like commutative property)? Is it provable? Is there a name for this?

I doubt this has a specific name but it is not hard to understand what is going on. In your example, you have the number $90+72*100+24*10000+...$. Each term in the sum is obviously divisible by 6, so the sum will be as well.