Suppose 600g of a radioactive substance are present initially and 3 years later only 300g remains. If the equation modelling the change in mass of the radioactive substance is y=y_(0)e⁽ᵏᵗ⁾. a. What is the initial mass of the radioactive substance? b. What is the value of k in the equation? c. How much of the substance will remain after 5 years?