You can put this solution on YOUR website!
This is just like the creation story in the Bible about ADAM and EVE. If you have like terms, then you must ADAM. If they are NOT like terms, then you must EVE them alone. (That was a joke!) Seriously, just combine like terms. The z terms are LIKE terms, so ADD them together. The x and z terms are NOT like terms, so LEAVE them alone.
(5x+ 3z) + 9z
5x + 12z
For additional help with topics like this, please see own my website by clicking on my tutor name "Rapaljer" anywhere in algebra.com. Then click on the link there to my website. From my Homepage, look for the link "Basic, Intermediate, and College Algebra: One Step at a Time." Look for "Basic Algebra" and look in Chapter 1. See Section 1.06 on Combining Like Terms and the Distributive Property. This is FULL of examples, exercises, and answers to all the exercises. See also the "Math in Living Color" pages where many of these exercises are solved IN COLOR. My own students used to tell me that my explanations are much easier to understand than the traditional textbooks. Perhaps you will like this section. I just want to make math easier for people who have trouble with math. It's usually not as hard as everyone thinks it is. The website has a lot of resources--all FREE.
Dr. Robert J. Rapalje, Retired
Seminole State College of Florida
Altamonte Springs Campus