A ball of mass $3$ kg moving with a velocity of $4$ m/s undergoes a perfectly-elastic direct-central impact with a stationary ball of mass $m$. After the impact is over, the kinetic energy of the $3$ kg ball is $6$ J. The possible value(s) of $m$ is/are

- $1$ kg only
- $6$ kg only
- $1$ kg, $6$ kg
- $1$ kg, $9$ kg