In 2011 a country's federal receipts (money taken in) totaled $2.12 trillion. In 2013, total federal receipts were $2.93 trillion. Assume that the growth of federal receipts, F, can be modeled by an exponential function and use 2011 as the base year (t = 0). a) Find the growth rate k to six decimal places, and write the exponential function F(t), for total receipts in trillions of dollars. b) Estimate total federal receipts in 2015. c) When will total federal receipts be $13 trillion? a) Find the growth rate k. k = (Do not round until the final answer. Then round to six decimal places as needed.) a) The cost of first-class postage stamp was 4 in 1962 and 40 in 2010. This increase represents exponential growth. Write the function S for the cost of a stamp t years after 1962 (t = 0). b) What was the growth rate in the cost? c) Predict the cost of a first-class postage stamp in 2015, 2018, and 2021. d) The Forever Stamp is always valid as first-class postage on standard envelopes weighing 1 ounce or less, regardless of any subsequent increases in the first-class rate. An advertising firm spent $4000 on 10,000 first-class postage stamps in 2009. Knowing it will need 10,000 first-class stamps in each of the years 2010-2022, it decides at the beginning of 2010 to try to save money by spending $4000 on 10,000 Forever Stamps, but also buying enough of the stamps to cover the years 2011 through 2022. Assuming there is a postage increase in each of the years 2015, 2018, and 2021 to the cost predicted in part (c), how much money will the firm save by buying the stamps? a) Choose the correct answer below. OA. S(t)=0.05e40t