Oxygen content of a pond when organic waste is dumped into

Question

Question: OXYGEN CONTENT OF A POND When organic waste is dumped into a pond, the oxidation process that takes place reduces the pond's oxygen content. However, given time, nature will restore the oxygen content to its natural level. Suppose the oxygen content t days after organic waste has been dumped into the pond is given by

f(t) = 100 (t² - 4t + 4)           (0 ≤ t < ∞)
                ( t² + 4 )

Percent of its normal level . Sketch the graph of the function f and interpret your results.