Need some help with a question regarding number sequences

[Joxu]

At which values of n is the decimal number 12n34n567n89n divisible by
a) 3
b) 6

An explain would also be appreciated.
I also accidentally marked this as solved, so don't mind that.

 

[Dr.Peterson]

The rule for divisibility by 3 is that the sum of all the digits must be a multiple of 3. For example, to test whether 18453 is divisible by 3, we add 1+8+4+5+3 = 21, which is a multiple of three, so 18453 is also.

So what value of n will make that happen?

Once you've answered that, consider that any multiple of 6 is a multiple of both 3 and 2.

Let us know what you find, so we can continue to help if needed.