Chapter 1.8, Problem 55E

Sales. The following graph represents the sales, y, of a new video game after t weeks on the market.

a. In what open interval(s) $f\text{'}\left(t\right)=0$?

b. In what open interval(s) $f"\left(t\right)=0$?

c. In what open interval(s) $f"\left(t\right)>0$?

d. In what open interval(s) $f"\left(t\right)<0$?

e. Describe in works and graphically the difference in meaning between “sales are increasing” and “the rate of sales is increasing.