$a)$

$D_f=\left\{2,3,4,5,6\right\}$

$Z{W}_f=\left\{-1,0,1\right\}$

$f\left(x\right)=0gdyx\in \left\{3,4\right\}$

$b)$

$D_f=\left\{-6,-4,-3,-1,-0,50,1,4\right\}$