Sophie spends a winter day recording the temperature once every three hours for
science class. At 9 am, the temperature was -1.7°F. Between 9am and noon, the
temperature increased by 18.1°F. Between noon and 3pm, the temperature increased
by 14.8°F. Between 3pm and 6pm, the temperature dropped 14.6°F. What was the
temperature at 6pm?