20. [1/3 Points] DETAILS PREVIOUS ANSWERS HARMATHAP12 9.8.041. The daily sales S (in thousands of dollars) that are attributed to an advertising campaign are given by 19 S = 7+ 3 t + 4 (t + 4)2 where t is the number of weeks the campaign runs. (a) Find the rate of change of sales at any time t. S' = || (b) Use the second derivative to find how this rate is changing at t = 15. (c) Interpret your result in part (b). The rate of change of the rate of change in sales (after 15 weeks) is the amount given in part (b). Need Help? Read It + Show My Work (Optional)? Submit Answer Submit Assignment Save Assignment Progress