Iodine 131 is a radioactive material that decays according to the function A(t) = A_0(e)^(-0.087t) where A_0 is the initial amount present and A is the amount present at time t (in days). Assume that a scientist has a sample of 100 grams of iodine 131.
Note: A_0 is read: "A sub zero"
(c) When will 70 grams of iodine 131 be left?
(d) What is the half-life of iodine 131?