Iodine -131 is a radioactive substance that decays at a rate of 8.3% every day. If a sample contains x grams of iodine -131 after 2 days, how much iodine -131 will it contain after 6 days?

After 2 days, the sample will contain:

x * (1 - 0.083)^2 = x * 0.7487

After 6 days, the sample will contain:
x * (1 - 0.083)^6 = x * 0.4482

Therefore, the sample will contain 44.82% of x grams of iodine-131 after 6 days.