A body $A$, of mass $m=0.1 \mathrm{~kg}$ has an initial velocity of $3 \hat{i} \mathrm{~ms}^{-1}$. It collides elastically with another body, $B$ of the same mass which has an initial velocity of $5 \hat{j} \mathrm{~ms}^{-}$ 1. After collision, A moves with a velocity $\vec{v}=4(\hat{i}+\hat{j})$. The energy of $B$ after collision is written as $\frac{x}{10} J$. The value of $x$ is $\_\_\_\_$ .