Limiting and Excess Reactants example $3$

In a test on a furnace fired with natural gas $($composition $95\%$ methane, $5\%$ nitrogen$)$ the following flue gas analysis was obtained: carbon dioxide $9\mathrm{.}1\%,$ carbon monoxide $0\mathrm{.}2\%,$ oxygen $4\mathrm{.}6\%,$ nitrogen $86\mathrm{.}1\%.$ All the percentages are by mol. Calculate the percentage of excess air flow $($percentage above stoichiometric$)$