{x+y=7
{2x+y=8
x=7-y
(7-y)2+y=8
14-2y+y=8
-y=8-14
-y=-6|:(-1)
y=6
x+6=7
x=7-6
x=1
{3m-2n=5
{m+2n=15
m=15-2n
3(15-2n)-2n=5
45-6n-2n=5
-8n=5-45
-8n=-40|:(-8)
n=5
m+5*2=15
m=15-10
m=5
{x-y=-2
{x-2y=4
x=-2+y
-2+y-2y=4
-y=4+2
-y=6|:(-1)
y=-6
x-(-6)=-2
x=-2-6
x=-8
{a+3b=2
{2a+3b=7
a=2-3b
(2-3b)2+3b=7
4-6b+3b=7
-3b=7-4
-3b=3|:(-3)
b=-1
a-1*3=2
a=2+3
a=5
{-x+y=0
{3x+y=8
y=x
3x+x=8
4x=8|:4
x=2
-2+y=0
y=2
{3k-5p=14
{k+2p=1
k=1-2p
(1-2p)3-5p=14
3-6p-5p=14
-11p=14-3
-11p=11|:(-11)
p=-1
k-1*2=1
k=1+2
k=4