Answer:
If in a equation there are numbers that have the same letters you can just add them or subtract them depending on the signs.
Explanation:
For example this equation:
2x + 7b - 7x + 9b + 1a - 22a
So you just put them in different categories(Remember to bring them with the sign that's in front of each number) after that you just add or subtract them
category x(only numbers that have x's go here): +2x-7x = -5x
category b (only numbers that have b's go here): +7b+9b = +16b
category a (only numbers that have a go here): +1s-22b = -21a
now just put them in the same equation:
-5x+16-21a
and done!^^
Hope this example helped~