A radioactive element decays according to the function Q - Q e ", where Do is the amount of the substance at time t- 0, r is the continuous compound rate of decay, t is the time in years, and Q is the amount of the substance at time t If the continuous compound rate of the element per year is r = =0.000145, how long will it take a certain amount of this element to decay to half the original amount? (The period is the half-life of the substance.) The half-life of the element is approximately years (Do not round until the final answer. Then round to the nearest year as needed.)