Chapter 6 - Section 6.8 - Exponential Growth and Decay Models; Newton's Law: Logistic Growth and Decay Models - 6.8 Assess Your Understanding - Page 486: 8

See below.

a) $N(t)=N_0e^{kt}$ b) We know that $800000=900000e^{k\cdot2}\\\frac{8}{9}=e^{2k}\\2k=\ln\frac{8}{9}\\k=\frac{\ln\frac{8}{9}}{2}\approx-0.05889151782819172726939705473526085253424035628236657055$ Thus $N(4)=900000e^{-0.05889151782819172726939705473526085253424035628236657055\cdot4}\approx711111$