Combining like terms is a process where you combine the terms with the same variable and/or exponent.
Let's say that we have an expression 3p + 3q. We can't combine the like terms, because 3p and 3q have different variables.
Now, what is the distributive property?
The distributive property is a property used for multiplying a monomial by a binomial or trinomial by "distributing" the monomial. The distributive property has a formula, which is:

Here, a got multiplied by b and c.
Similarly, we combine the terms:

Simplify:

Combine like terms:

Hence, the simplified answer is 7x - 6.