Suppose that a cup of soup cooled from 90 °C to 60 °C after 15 minutes in a room whose temperature was 20 °C. Use Newton's law of cooling to answer the following questions.
(a) How much longer would it take the soup to cool to 45 °C?
(b) Instead of being left to stand in the room, the cup of 90 °C soup is put in the freezer whose temperature is - 15 °C. How long will it take the soup to cool from 90 °C to 45 °C?