Newton's law of cooling describes that the temperature of object changes at a rate proportional to the difference between its temperature and that of its surroundings. Assume that the temperature of a cup of coffee obeys Newton's law of cooling. If the coffee has a temperature of 210 degrees Fahrenheit when freshly poured, and 1.5 minutes later has cooled to 193 degrees in a room at 72 degrees, determine when the coffee reaches a temperature of 168 degrees.
The coffee will reach a temperature of 168 degrees in how many minutes?