Gas Nitrous Oxide (N20) is used as an anesthetic and in aerosol cans to produce whipping cream. It is a potent greenhouse gas and decomposes slowly to N2 and O2.
2 N2O(g) --> 2 N2(g) + O2(g)
How many half-lives will it take for the concentration of the N20 to reach 3.13% of its original concentration?