Question

I don't really understand, if someone could help that would be great

Answer 1

When combining like terms, always go from left to right.

7x-8x = -1x
9y-4y-5y=0
answer is -1x

Answer 2

Simplifying   7x+9y+-8x+-4y+-5y=0

reorder the terms   7x+-8x+9y+-4y+-5y=0

combine like terms  7x+-8x=-1x-1x+9y+-4y+-5y=0

 combine like terms  9y+-4y=5y-1x+5y+-5y=0

combine like terms 5y+-5y=0
-1x+0=0
-1x=0

solving
-1x=0