Chapter 8, Problem 16P

The concentration of pollutant bacteria c in a lake decreases according to

$c=70e^{-1.5t}+25e^{-0.075t}$

Determine the time required for the bacteria concentration to be reduced to 9 using (a) the graphical method and (b) using the Newton-Raphson method with an initial guess of $t=10$ and a stopping criterion of 0.5%. Check your result.