How is subtracting-4x from 9x similar to subtracting -4 from 9?

Question:

How is subtracting -4x from 9x similar to subtraction -4 from 9?

If both of them have the same variable lets say this:

2a + 2a = 4a
Just add 2 + 2 and then keep the a later at the end since they both have the same letter.

So in this case, it will be the same as subtracting -4 from 9 because they both have the same variables so the x would stay the same:

-4x + 9x = 5x 
would be the answer.

Hope this helped! 

~Shane