84. Oxygen Content of a Pond The oxygen content t days after organic waste has been dumped into a pond is given by + 10t + 100 f (t) = 100 12 + 20t + 100 percent of its normal level. a. Show that f (0) = 100 and f (10) = 75. b. Use the Intermediate Value Theorem to conclude that the oxygen content of the pond must have been at a level of 80% at some time. c. At what time(s) is the oxygen content at the 80% level? Hint: Use the quadratic formula