Iodine 131 is a radioactive material that decays according to the function A(t) = A₀e^-0.084t, where A₀ 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.

(a) What is the decay rate of iodine 131?

(b) How much iodine 131 is left after 9 days?

(c) When will 70 grams of iodine 131 be left?

(d) What is the half-life of iodine 131?