A publishing company estimates that when a new book by a best-selling author is introduced, its sales can be modeled as n(x) = 68.99x thousand books sold in the United States by the end of the xth week. Sales outside the United States can be modeled as a(x) = 0.121x thousand books sold by the end of the xth week. (a) Write a formula for the total number of copies t sold by the end of the xth week. t(x) = thousand books (b) Write the rate-of-change formula for the total number of copies sold by the end of the xth week. t'(x) = thousand books per week (c) How many copies of the book will be sold by the end of 52 weeks? (Round your answer to three decimal places.) thousand books (d) How rapidly are books selling after 52 weeks? (Round your answer to three decimal places.) thousand books per week Write the answer in a sentence of practical interpretation. At the end of 52 weeks, sales are ---Select-- by thousand books per week. Need Help? Read It