like terms are term that has the same variable
Ex: 5a and 19a are like terms because they have they same "a" varaible
You can simplify like terms only by add or subtract the numbers like terms
Ex:

in this case,

and

are like term so we add them together, 4+5= 9, so

, is simplified answer.
Then

and

are like terms again so we also add them together, 2+9 =


is alone so you just keep it the same, remember your negative sign.
The answer will be:

Hoped it helped