Dear Student ,
We know that the momentum is always conserved if there is no external force
Here all the forces are internal so we can apply momentum conservation
initially the mass was M=300 g and initial speed , u=0
Now the mass M is broken into two parts M1 and M2
And the velocities respectively is v1 =12m/s towards east and v2
where M1=200g and M2=100 g
Now apply the conservation principle ,
Here negative sign indicates that the velocity of second particle is opposite to the direction of first particle .
So the second particle is moving at a speed of 24m/s towards west .
Regards