Answer: The like terms are 12, 5, -4, 1...
I know this because none of them have a variable, and because i just learned this a few months ago, (and got an A...)
The 15 with the variable do not have like terms because it has a variable and none of the other number do...
Sorry if this doesn't make sense.. Hope this helps... Stay safe and have a great day/night!!! :D