The amount Q, in mg, of a radioactive substance that is present at time t, in years, is given by the formula Q = 90(0.5) a) How much is present initially? b) Find the half-life and use the half-life to complete the table. c) By what percent does Q decay each year? a) The amount that is present initially is mg b) The half-life of the radioactive substance is years. Use the half-life to complete the table. t (years) Q (mg) O 22.5 11.25 c) The substance decays by 1 % per year. (Type an integer or decimal rounded to one decimal place as needed.)