Answer:
20 years
Step-by-step explanation:
Amortization refers to the process of lowering book value in case of intangible assets or services such as copyrights, trademarks , patents, etc.
It simply refers to spreading the cost of an intangible asset over it's estimated life.
A patent refers to an exclusive right to use a certain technology or a method which cannot be used by anybody else.
As per US Generally accepted accounting principles, patents are to be amortized over period of their estimated benefits or a period of 20 years whichever is earlier.
This means the amortization of patents cannot exceed a period of 20 years.