a) $3x+yi=2y+1+(2-x)i$

<=> $\left\{\begin{matrix}3x=2y+1 & \\ y=2-x & \end{matrix}\right.$

<=> $\left\{\begin{matrix}x=1 & \\ y=1 & \end{matrix}\right.$

Vậy $\left\{\begin{matrix}x=1 & \\ y=1 & \end{matrix}\right.$

b) $2x+y-1=(x+2y-5)i$

<=> $\left\{\begin{matrix}2x+y-1=0 & \\ x+2y-5=0 & \end{matrix}\right.$

<=> $\left\{\begin{matrix}x=-1 & \\ y=3 & \end{matrix}\right.$

Vậy $\left\{\begin{matrix}x=-1 & \\ y=3 & \end{matrix}\right.$