Let be the time in weeks. At time , organic waste is dumped into a pond. The oxygen level in the pond at time is given by
Assume is the normal level of oxygen.
(a) On a separate piece of paper, graph this function.
(b) What will happen to the oxygen level in the lake as time goes on?
(c) Approximately how many weeks must pass before the oxygen level returns to % of its normal level?
weeks (Round to at least two decimal places.)