Solving systems equations by elimination -2x-9y=-25 -4x-9y=-23 x-y=11 2x+y=19 -4x-2y=-12 4x+8y=-24 5x+y=9 10x-7y=-18

I won't answer them all for you (don't want to cheat - need to learn something).
But for the first one given:

-2x-9y=-25
-4x-9y=-23

you set up either x or y (which ever one you want to eliminate) so that one of them cancels.
So this one is easy - you just have to multiply an entire row by negative (doesn't matter which one) - so that the y's will be + and - 

Since they're both 9 and they're subracting NOW - you can eliminate the y value. Now add/subtract the x's. So it'd be -2 or 2 depending on how you eliminated y. Then add the number outside of the = sign. Now just solve for x. After that plug in whatever you got for x into both of the rows. Then find the y value.

Hopefully this wasn't confusing -- reply if it is and I will try to simplify. I can give you contact if you need help with the rest 

Good luck!