a) 6x+4=2x+12
4*x+4-12=0
4*x-8=0
x=8/4
x=2
б) 4*(2x+1)+x=2x+25
8*x+4+x-2*x-25=0
9*x+4-2*x-25=0
7*x+4-25=0
7*x-21=0
x=21/7
x=3
в) 5/18*(0,54-7,2y)-4/19*(0,76-3,8y)=0,002
(5/18)*(0.54-7.2*y)-4/19*(0.76-3.8*y)-0.002=0
0.15-2*y-4/19*(0.76-3.8*y)-0.002=0
0.15-2*y-(4/19)*(0.76-3.8*y)-0.002=0
0.15-2*y-(0.16-0.8*y)-0.002=0
0.15-2*y-0.16+0.8*y-0.002=0
-0.01-2*y+0.8*y-0.002=0
-0.01-1.2*y-0.002=0
-0.012-1.2*y=0
y=-0.012/1.2
y=-0.01