Three balls

Three balls $A, B, C$ of respective masses $5\text{ kg}, 5 \text{ kg}, 20 \text{ kg}$ stand in a row in that order.

Now, ball $A$ moves towards $B$ at speed $1\text{ m/s}$ while $B$ and $C$ are still at rest. There aren't any frictional forces, and the collision between balls $A$ and $B$ are perfectly elastic.

If the final velocity of ball $C$ is $0.4\text{ m/s},$ what will be the final speed $($ in $\text{m/s})$ of ball $A,$ to 1 decimal place?