On to the 3rd one. You should be getting the gist of it now.
7.
x - y = -3
x - y = 1
Looks like some simple stuff. Multiply one of the equations by -1, put it back in... but wait. If you do so, you'll eliminate both variables? Don't believe me? go try.
The thing is, this just does not work... I'll assume (based on the answer key), that it would be better to try to solve
x + y = -3
x - y = 1 If not, my apologies.
Do your basic addition/elimination to get
2x = -1
x = -1
Apply this:
-1 - y = 1
-y = 2
y = -2
Now for the last one.
9.
3m - 2n = 13
m + 2n = 7
Do as I have told you to do for the past three times. You've probably got this down by now, so I'll make the explaining short
4m = 20
m = 5
Apply back
5 + 2n = 7
2n = 2
n = 1
Hope this helps!