4-(5+y)+(7-2y)=4-5-y-7+2y 4+(5-y)-(7-2y)=4+5-y-7-2y
4-(5+у)+(7-2у)=4-5-y-7+2y 4-5-y+7-2y=-8+y 6-3y=-8+y 4y=14 y=14/4 y=3,5 4+(5-y)-(7-2y)=4+5-y-7-2y 4+5-y-7+2y=2-3y 2+y=2-3y y+3y=2-2 4y=0 y=0/4 y=0