The data obtained from an air sample analysis of an old working in a coal mine are given.

O₂ 17.15%, CO₂ 3.40%, CH₄ 2.20%, and N₂ 77.25%.

Considering atmospheric air contains O₂ 20.95%, CO₂ 0.03%, and N₂ 79.02%, the percentage of blackdamp in the old working, is _____. (round off up to 2 decimals)