Add:- $a + b - 3,b - a + 3,a - b + 3$

Hint: For solving such types of questions first write what you have been given. Here there are three values and we have to add them. So as we solve normal number addition questions, in these types of questions we need to do the same.

Complete step by step answer:
In these questions we need to find an addition of given three values.
So first we will write that three values:
 $ \Rightarrow a + b - 3,b - a + 3,a - b + 3$
Now, for addition of these value we will add them,
$ \Rightarrow a + b - 3 + b - a + 3 + a - b + 3$
Now, we will write together all a, b and three.
$ \Rightarrow a - a + a + b + b - b - 3 + 3 + 3$
After simplifying we get,
$ \Rightarrow a + b + 3$

So, the answer of this question is $a + b + 3$

Note:
For solving these types of questions is very easy all you have to do is just write those values and after that add them. Here we have three values and all have a, b and a number. So after that we will write them together and add them. This is a simple addition question but many students just read the question and ignore it. So try to understand the question and after you start solving.