2. The amount of a radioactive element at time t is given by the formula A(t)= A0ekt, (1) where A(0)= A0 is the initial amount of the element and k < 0 is the constant of proportionality which satisfies the equation (instantaneous rate of change of A(t) at time t) = kA(t). Iodine–131 is a commonly used radioactive isotope used to help detect how well the thyroid is functioning. Suppose the decay of Iodine–131 follows the model given in Equation (1), and that the half–life of Iodine–131 is approximately 10 days. If 5 grams of Iodine– 131 is present initially, find a function which gives the amount of Iodine–131, A, in grams, t days later, and then after 20 days.