Example 7: The radioactive element Plutonium-239 (2Pu ) has a half-life of 24,360 years. Suppose that a sample of this substance has a mass of 100 mg. (a) Find a function with base 2 that models the mass of this substance after f-years. (b) Find a function with base e that models the mass of this substance after /-years. (c) What is the mass of the substance after 1,000 years? (d) how long will it take for the mass of this substance to reach 40 mg