By definition, the like terms in a mathematical expression are those terms that have the same variables and the same exponents.
For this case, you have the following expression given in the exercise:
You can identify that the terms in the expression are like terms, because they have the same variable "p", and the same exponent 1. In order to add them (or combine them), you must follow this procedure:
1. You need to apply the Sign rules for multiplication. Remeber that:
Then:
2. Since both terms have the same sign, you must add the coefficients and rewrite the variable and the negative sign.
Then, you get that the answer is: