Conversation so far:
What was the Reciprocity Treaty of 1875?
This free trade agreement between the United States and Hawaii allowed sugar and other products to be exported to the US duty free
How did the Reciprocity Treat affect the people of Hawaii?
Over the term of Kalākaua's reign, the treaty had a major effect on the kingdom's income.
How long did the Reciprocity Treaty last?
A seven-year treaty was signed on January 30, 1875
What happened after the seven-year Reciprocity Treaty ended?
When it expired, an extension of the treaty was negotiated, giving exclusive use of Pearl Harbor to the United States.

Question: How long was it extended?
Self-contained rewrite: How long was the Reciprocity Treat extended?