Question

Polluted water from a factory flows into a pond. The concentration of pollutant,
c, in the pond at time t minutes is modelled by the equation
c(t)=8-8000(1/1000+2t)

where c is measured in kg/m3. When will the concentration of pollutant in the
pond reach 6 kg/m3?

Answer 1

you want t when c=6

8-8000(1/1000+2t) = 6
8000(1/1000+2t) = 2
(1/1000+2t) = 2/8000
1/1000 + 2t = 1/4000
2t = 1/4000 - 1/1000
2t = -3/4
Bzzt

You must have meant

8-8000(1/(1000+2t)) = 6
8000(1/(1000+2t)) = 2
1/(1000+2t) = 1/4000
1000+2t = 4000
2t = 3000
t = 1500

that's just over 1 day.