Business: Advertising An automobile dealership finds that the number of cars that it sel...

Business: Advertising An automobile dealership finds that the number of cars that it sells on day x of an advertising campaign is S(x) = -x²+10x (for 0 ≤ x ≤ 7).

a. Find by using the definition of the derivative.

b. Use your answer to part (a) to find the instantaneous rate of change on day x = 3.

c. Use your answer to part (a) to find the instantaneous rate of change on day x = 6. Be sure to interpret the signs of your answers.