Respuesta :

I'm only going to answer #18. I'm sorry but that is too much work for too little points. If you re-post the questions separately I might have a go at them

18.  x + y =  0

-2x -y = 8

y = -x so...

-2x - (-x) = 8

-2x + x = 8

-x = 8

x = 8

y = - x

y = -8

Hope this helped!