Apiece of interstellar debris (with mass m and moving at speed v relative to a deep-space observer) explodes into two pieces, one of them 3 times as massive as the other. the less massive piece stops as seen by the observer (in the observer's frame of reference).

how does the kinetic energy of the system change as a result of the explosion, as seen in the observer's frame of reference? express your answer as a ratio of the change in kinetic energy to the initial kinetic energy.

your answer should be unitless since it is a ratio.