3rd ball says: Ouch It Hurts!

Three balls are kept on a straight line on a smooth surface. The first ball of mass ${ m }_{ 1 }$ is projected with velocity ${ V }_{ o }$ towards the middle ball of mass ${ m }_{ 2 }$, which then collides with the third ball of mass ${ m }_{ 3 }$.

If we want ${ m }_{ 3 }$ to move with the maximum possible velocity, then what should be the mass of ${ m }_{ 2 }$ in kg? All collisions are elastic.

$\textit{Details}$

Use the following data if needed :

$\bullet \quad { m }_{ 1 }\quad =\quad 4\quad kg \\ \bullet \quad { m }_{ 3 }\quad =\quad 9\quad kg \\ \bullet \quad { V }_{ o }\quad =\quad 16\quad m/s$