A building is found to contain a radioactive gas. Thirty hours later, 75% of the initial amount of gas is still present. (Note: Use the concepts of half-life or doubling time.) (a) Write a model for the percentage of the initial amount of the radioactive gas present after 1' hours. (Round all numerical values to three decimal places.) r(f) = 0.959 % X (b) Calculate the half-life of the radioactive gas. (Round your answer to three decimal places.) 722.781 x hours