38. Radon-222 has a half-life of about 3.8 days. a. What is the decay factor? b. Write an exponential function of the form A(t) = A,e* if there was originally 8 grams. 39. A bone fragment is found that contains 20% of its original carbon-14. To the nearest year, how old is the bone? (The half-life of carbon-14 is 5730 years.)