A cup of boiling water (212∘F) is placed to cool in a room whose temperature remains constant at 68∘F. Suppose the difference between the water temperature and the room temperature is halved every 5 minutes. What is the water temperature, in degrees Fahrenheit, after 15 minutes?
<spanclass=′latex−bold′>(A)</span>77<spanclass=′latex−bold′>(B)</span>86<spanclass=′latex−bold′>(C)</span>92<spanclass=′latex−bold′>(D)</span>98<spanclass=′latex−bold′>(E)</span>104