Determine the percent excess air used

Question

A natural gas analyzes N₂, 20.0 percent and CH₄, 80.0 percent and it is burned under a boiler and most of CO₂ is scrubbed out of the flue gas for the production of dry ice. The exit gas from the scrubber analyzes O₂ 4.9 percent; N₂, 93.9 percent and CO₂, 1.2 percent. Determine the

1. Percent excess air used.

2. Percentage of the CO₂absorbed.