A polluted lake has an initial concentration of bacteria of 10^7 parts/m^3, while the acceptable level is only 5x10^6 parts/m^3. The concentration of the bacteria will reduce as fresh water enters the lake. The differential equation that governs the concentration C of the pollutant as a function of time (in weeks) is given by:
Using Euler's method and a step size of 3.5 weeks, find the concentration of the pollutant after 7 weeks.