A cup of boiling water (212 \, \text{°F}) is placed to cool in a room whose temperature remains constant at 68 \, \text{°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?
Answer Choices
A. 77
B. 86
C. 92
D. 98
E. 104