Answer
$v_{cm}=+2m/s$
The positive sign indicates that the velocity is directed to the right.
Work Step by Step
We have $$v_{cm}=\frac{m(+4m/s)+m(-8m/s)+2m(+6m/s)}{m+m+2m}$$ $$v_{cm}=\frac{4m-8m+12m}{4m}$$ $$v_{cm}=+2m/s$$
The positive sign indicates that the velocity is directed to the right.
