Answer
The velocity of the center of mass is $~5~m/s~$ toward the west.
Work Step by Step
Let west be the positive direction.
We can find the velocity of the center of mass $v_{com}$:
$v_{com} = \frac{(5.0~kg)(-10~m/s)+(15~kg)(10~m/s)}{5.0~kg+15~kg} = 5~m/s$
The velocity of the center of mass is $~5~m/s~$ toward the west.
