I’m not exactly sure that my answer is accurate. However, when you are combining like terms you have to add the terms that are similar... hopefully that makes sense.
For example:
2x + 7 + 8x + 3
What you want to do is simply the expression
We can see that 2x and 8x are both coefficients
(A coefficient is a number that is going to be multiplied by a variable such as 3y, 2x, 7x and so on)
They are both like terms meaning that they can be combined
2x + 8x= 10x
Next, you want to see if you can combine anything else because our goal is to make the expression simplified.
7 and 3 can be combined because they are like terms
7+3= 10
Now that you have the new numbers I guess you can call it your answer should be
10x + 10
Hopefully this helps you answer the other questions. I did this lesson not too long ago so if you need help on anything else I can try to explain it.