$\left ( 268 \right )_{10}=\left ( 1124 \right )_{6}$
$5^{s}$ complement of $\left ( 1124 \right )_{6}$=$\left ( 5555-1124 \right )_{6}=\left ( 4431 \right )_{6}$
$\Rightarrow 6^{s}$ complement =$\left ( 4431 +1\right )_{6}$=$\left ( 4432 \right )_{6}$