3different ways in which carbon is added to the atmosphere by natural means

(The 3 examples are:)

~ CO2 from burning fossil fuels

 ~ gas (methane) leaks from underground gas pipes

~ methane from rotting material in landfills

(Other ones)
~ combustion of fossil fuels (oil, coal, and gas)

~ deforestation (decreasing amount of plants that remove CO2 from the atmosphere)

~ industrial production that uses petroleum based products (mineral/metal production)

the answer would be   10%