Solve the Problem $S(t)=150-90 e^{-.7 t}$ , Where $t$ Represents Time in Years

Multiple Choice

Solve the problem.
-The sales in thousands of a new type of product are given by $S(t) =150-90 e^{-.7 t}$ , where $t$ represents time in years. Find the rate of change of sales at the time when $t=2$ .

A) 15.6 thousand per year
B) -254.4 thousand per year
C) 2 54.4 thousand per year
D) -15.6 thousand per year