The sales of a new personal computer (in thousands) are given by
$$S(t)=100-90 e^{-0.3 t}$$
where $t$ represents time in years. Find the rate of change of sales at each time.
a. After 1 year
b. After 5 years
c. What is happening to the rate of change of sales as time goes on?
d. Does the rate of change of sales ever equal zero?