$\text{a)}4x-2m=2\left(x+m\right)-2\mid :2$  

$2x-m=x+m-1$  

$x=2m-1$  

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$\text{b)}4x-2m=2\left(x+m\right)-2\mid :2$  

$2x-m=x+m-1$  

$-2m=-x-1\mid :\left(-2\right)$  

$m=\frac{x+1}{2}$