For this, you would need to combine your like terms
In this case your like terms are 4a and 5a : 7b and -b
So, all you do is add
4a + 5a= 9a
7b + (-b) or if it is easier to understand you can write it as 7b - b
When adding these two together, b contains an invisible one in front of it so if you feel the need to, you can also write the equation as:
7b + (-1b) or 7b - 1b
7b - 1b= 6b
Your answer is 9a + 6b
Side note: anytime you have a single variable ( just a or b or x) any single variable with no number in front of it, that means there is an invisible one in front of it ( 1a or 1b or 1x)
Hope this helps :)
