The amount of a sample remaining after t days is given by the equation p(t)=a(1/2)^(t/h), where a is the initial amount of the sample and h is the half-life, in days, of the substance. a sample contains 18% of its original amount of radon-222. the half-life of radon-222 is about 3.8 days. which is the best estimate for the age of the sample?