From mass ratio 2:2:3 with total mass 14 kg: individual masses are 4 kg, 4 kg, and 6 kg.
Setting coordinate axes along the motion directions of the two equal fragments: fragment 1 has momentum p1=4×18i^=72i^ kg⋅m/s, and fragment 2 has p2=4×18j^=72j^ kg⋅m/s.
By momentum conservation, initially at rest: p1+p2+p3=0, so p3=−72i^−72j^ kg⋅m/s.
Velocity of 6 kg fragment: v3=6p3=−12i^−12j^ m/s.
Speed: ∣v3∣=144+144=288=122 m/s.