4
5x - 4 = 16
Add four to both sides
5x = 20
Divide both sides by 5
x = 4
<h2>
Hello!</h2>
The answer is:

<h2>
Why?</h2>
To solve the problem we need to add/subtract like terms. We need to remember that like terms are the terms that share the same variable and the same exponent.
For example, we have:

We have that we were able to add just the terms that were sharing the same variable and exponenr (x for this case).
So, we are given the expression:

Hence, the answer is:

Have a nice day!