smc

If the three numbers are in proportion to $2:4:6$, then they should also be in proportion to $1:2:3$. This implies that the three numbers can be expressed as $x$, $2x$, and $3x$. Add these values together to get: $$x+2x+3x=6x=64$$ Divide each side by 6 and get that $$x=\frac{64}{6}=\frac{32}{3}=10\frac{2}{3}$$ which is $\boxed{10\frac{2}{3}}$.