The population of Americans age 55 and older as a percentage of the total population is approximated by the function f(t) = 10.72(0.9t + 10) 0.3 (0 t 20) where t is measured in years, with t = 0 corresponding to 2000.+ Compute f"(9). (Round your answer to three decimal places.) f"(9) = Interpret your result. Find the first and second derivatives of the function. f(u) = 12 - 5u f'(u) f"(u) = =