1. a+b-5-b+7-a=a-a+b-b+7-5=2
8-18+m-n-m+n=m-m+n-n+8-18=-10
x-y+5-4-x+y=x-x+y-y+5-4=1
2. 30-m+7-9=-5
-m=-5-30-7+9
-m=-33
m=33
n-5+6-10=0
n=5-6+10
n=9
-6+8-10-x=-3
-x=-3+6-8+10
-x=5
x=-5
3. 4n-2(n+7)=2n-2(n-1)
4n-2n-14=2n-2n+2
4n-2n-2n+2n=2+14
2n=16
n=8