A company's weekly sales (in thousands) after x weeks are given by ...

A company's weekly sales (in thousands) after x weeks are given by
 

f (x) = x³- 3x²- 9x + 7
 

thousand dollars (for x ≥ 0).
 

a) Make sign diagrams (sign charts) for the first and second derivatives.
 

b) Sketch the graph of the sales function, showing all relative extrema points and inflection points. State domain, and label and interpret the y-intercept