Answer: It will take 3.75 hours to reach 20°C.
Solution:
The bottle temperature begins at the freezer temperature of –16° C
How many hours will it take to reach 20° C?
Change in temperature=20°C – (–16°C)
Change in temperature=20°C+16°C
Change in temperature=36°C
The bottle temperature will go up a steady 9.6° C every hour. Using a rule of three:
9.6°C → 1 hour
36°C → x
x=(36°C)(1 hour)/(9.6°C)
x=3.75 hours
Answer: It will take 3.75 hours to reach 20°C.