How do you simplify #8.7g + 15.43g + 19g#?
You can think of this question as like asking "if you had 19 apples, 15.43 apples and 8.7 apples, how many apples do you have total?".
Of course, the answer would just be to add up all the numbers you have, and that's how many apples you have.
We're doing the same thing when we simplify this. You simply add up all the terms, and that's how many
Hope this helps :-)