Recall that two terms are called like terms if the variables in the terms are the same and have the same exponents, meaning they can be added or subtracted.
For example, 3x and 6x are like terms because the variable x is the same for both terms, and when adding those terms I get a simplified version of the expression:
Now, if instead, I have 3x and 6y, the variable is not the same, so when adding them I get:
there is no way to simplify the sum. 3x and 6y are not like terms.
Therefore, the only like term to 3 in the given options is 7.
Answer: 3 and 7 are like terms.