Newton's law of cooling states that the temperature of an object changes at a rate proportional to the difference between its temperature and that of its surroundings. Suppose that the temperature of a cup of coffee obeys Newton's law of cooling. If the coffee has a temperature of 184 °F when freshly poured, and 1 min later has cooled to 174 °F in a room at 70 °F, determine when the coffee reaches a temperature of 138 °F. Note: Enter the exact symbolic expression for the asked time. The coffee reaches the temperature 138 in _____ minutes.