upper lake has a volume of 50km3 and lower lake a volume of 100km3 . a river flows into upper lake, then connects the two lakes, and then flows out of lower lake. the river has a flow rate of 3km3 per day. suppose 2m3 of a pollutant was spilled into upper lake. the beach resort, located on the shore of lower lake, has hired you as a consultant. they want to know whether they need to close the beach. according to health guidelines, if the concentration of this particular chemical exceeds 0.008 ppb (parts per billion), then the beach must be closed for swimming and any other recreational activity. do you think the resort will need to close the beach? if so, for how long will be beach need to be closed?