A chemical substance has a decay rate of 8.6% per day. The rate of change of an amount N of the chemical after t days dN is given by = - 0.086N. dt a) Let No represent the amount of the substance present at t = 0. Find the exponential function that models the decay. b) Suppose that 400 g of the substance is present at t = 0. How much will remain after 3 days? c) What is the rate of change of the amount of the substance after 3 days? d) After how many days will half of the original 400 g of the substance remain? . . . a) N(t) =