Analysis of a sample of coal showed, it consists of $82$ wt$.\%$ of carbon, $5$ wt$.\%$ of water,

$2$ wt$.\%$ of hydrogen, $1$ wt$.\%$ of oxygen and $10$ wt$.\%$ of ashes. What amount of air is needed

to burn $1$ kg of coal in case the air has to be used in $20\%$ excess?