Please answer and explain each thoroughly. Thank you!

66. WORKER EFFICIENCY An efficiency study of the morning shift at a certain factory indicates that an average worker who arrives on the job at 8:00 A.M. will have assembled f(x) = -x3 + 6x2 + 15x television sets x hours later. a. How many sets will such a worker have assembled by 10:00 A.M.? [Hint: At 10:00 A.M., x = 2.] b. How many sets will such a worker assemble between 9:00 and 10:00 A.M