iodine-131 is a radioactive isotope that is a by-product of emissions of other radioactive isotopes. after the 2011 earthquake in japan that damaged server also nuclear reactors, high levels of iodine-131 were found near the nuclear power plants. iodine-131 has a half life of 8 days. if authorities found an original sample of 2.5 grams right after an emission from the plant, how much iodine-131 would be left 30 days later?