As you get higher the atmospheric pressure lowers. The pressure in the packet of crisps has the pressure at which it has been closed (pressure at the surface of the earth). This means that the air molecules in the packet press harder outside than the air molecules in the atmosphere press on the packet.
Answer: Infusion time is 5.5 h
Explanation: Time is 470 ml / 85 ml/h = 5.5 h
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