One January morning in 1943, a warm chinook wind rapidly raised the temperature in Spearfish, South Dakota from below freezing to +12.0°C. As the chinook died away, the temperature fell to -20.0°C in 27.0 minutes. Suppose a 24.7-m aluminum (α = 23x10-6 (C°)-1) flagpole were subjected to the temperature change. Find the average speed at which its height would decrease, assuming the flagpole reacted instantaneously to the changing temperature.