a.70 -5.(x-3)=45
x-3=70-5-45
x-3=20
x=20-3=17
b.2x-138=8.9
2x-138=72
2x=72+138
2x=210
x=210:2=105
c.10+2n=16
2n=16-10
2n=6
n=6:3=2
d.[(4x+28).3+55]:5=35
[(4x+28).3+55]=35x5=175
4x+28=(175-55):3
4x+28=40
4x=40-28=12
x=12:4=3
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