А.
10-((2х+1)-х)=3х
10-(2х+1-х)=3х
10-(х+1)=3х
10-х-1=3х
-х-3х=-9
-4х=-9
х=9:4
х=2,25
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Б
2/3(7-2х)=1/2
7-2х=1/2:2/3
7-2х=1/2×3/2
7-2х=3/4
2х=7-3/4
2х=6 4/4-3/4
2х=6 1/4
х=25/4÷2
х=25/4×1/2
х=25/8
х=3 1/8
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В
-4(х-10)=12(х-1)
-4х+40=12х-12
-4х-12х=-12-40
-16х=-52
х=52÷16
х=3,25