Answer
a. $0.014$
b. $73\ words$
c. $144\ min$
Work Step by Step
a. Use the given equation and conditions, we have $20=300(1-e^{-5k})$; thus $k=-\frac{ln(1-20/300)}{5}\approx0.014$
b. For $t=20$, we have $L(20)=300(1-e^{-0.014(20)})\approx73\ words$
c. Let $L=260$, we have $260=300(1-e^{-0.014t})$; thus $t=-\frac{ln(1-260/300)}{0.014}\approx144\ min$
