Momentum — practice question

Two particles $A$ and $B$ have masses $km$ and $m$ respectively, where $k$ and $m$ are constants, and are free to move in a straight line on a smooth horizontal plane. Particle $A$ is projected towards $B$ with speed $2u$ and, at the same instant, $B$ is projected towards $A$ with speed $u$. The particles collide. After the collision, $A$ moves with speed $u$ and both particles travel in the same direction as $A$ was originally moving. It is given that $35\%$ of the total kinetic energy is lost in the collision.