Answer:
12x, 15x, -x, and x are like terms.
Explanation:
These are terms that can be combined together in equations because they are multiplied by the same term or they are integers, etc. (BTW, I'm not sure if 3x2 means 3 times 2 or 3 times x times 2, if it is 3 times x times 2, then that is also a like term!)