Q3 (10 points) (a) Suppose that there is an initial amount An of a substance and that it decays at exponential rate so that only 65% of the substance remains after two hours. Find the time t in hours when only 50% of the initial amount remains. (b) Find with verification the dimensions of the rectangle of largest area such that its top two vertices lie along the parabola y = 9 - x and its bottom two vertices lie along the x-axis