Let two masses m$1=200$ g and m$2=400$ g $\mathrm{.}6$encounter an elastic one dimensional head$-$on collision. If v$1$i$=6\mathrm{.}0$ m$/$s in $+$x$-$axis and v$2$i$=0$ then the final total kinetic energy equals to: $(1$g$(=101-3$ kg