=2х-2х-у+у=0
=-а+2а-в+2в=а+в
=7-в-14-2в=-3в-7
=3в-18-в+8=2в-10
-----------------
=-7+х+3х-14=4х-21
=-х-4-2х+8=4-3х
=21-а-20+2а=1+а
=-13-в-в-13=-26-2в
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=6-2х-8-х=-2-3х
=-4у-20+12-у=-5у-8
=-7+х+4х-20=5х-27
=-9у+36-12-у=24-10у
1)321+(x+13)=450
321+x+13=450
x=450-321-13
x=116
2)240-(x+29)=100
240-x-29=100
x=240-29-100
x=111
3)122+(y-7)=200
122+y-7=200
y=200-122+7
y=85
4)53-(y-13)=24
53-y+13=24
y=53+13-24
y=42