Suppose there are two lakes located on a stream. clean water flows into the first lake, then the water from the first lake flows into the second lake, and then water from the second lake flows further downstream. the in and out flow from each lake is 500 liters per hour. the first lake contains 100 thousand liters of water and the second lake contains 200 thousand liters of water. a truck with 500 kg of toxic substance crashes into the first lake. assume that the water is being continually mixed perfectly by the stream. a) find the concentration of toxic substance as a function of time in both lakes. b) when will the concentration in the first lake be below 0.001 kg per liter? c) when will the concentration in the second lake be maximal?