When food supplies have been exhausted, populations die away. This exponential decay is described by a simple modification of the exponential growth model, Engineers use this model to calculate the length of time that a swimming beach must remain dosed following pollution with fecal material. For a population of bacteria with an initial biomass of 100 mg/L and a kd = 0.4 day-1, calculate the time necessary to reduce the population size to 10 mg/L.