A sample of 500 g of radioactive lead-210 decays to polonium-210 according to the function A(t) = 500e 0.032t, where t is time in years. Find the amount of radioactive lead remaining after (a) 4 yr, (b) 8 yr, (c) 20 yr. (d) Find the half-life. (a) The amount of radioactive lead remaining after 4 yr will be (Round to the nearest integer as needed.) g. (b) The amount of radioactive lead remaining after 8 yr will be (Round to the nearest integer as needed.) g. (c) The amount of radioactive lead remaining after 20 yr will be (Round to the nearest integer as needed.) g. (d) The half-life is about yr. (Round to two decimal places as needed.)