Use the References to access important values if needed for this question. Radioactive decay can be described by the following equation lnA=lnA0kt where A0 is the original amount of the substance, A is the amount of the substance remaining after time t, and k is a constant that is characteristic of the substance. For the radioactive isotope strontium-80, k is 4.08101 hours 1. If the original amount of strontium- 80 in a sample is 39.6mg, how much time is needed for the amount of strontium- 80 that remains to fall to 19.8mg ? hours