Conversation so far:
What was the Reciprocity Treaty of 1875?
a free trade agreement between the United States and Hawaii, that allowed sugar and other products to be exported the US to be duty free.
How did this affect the people of Hawaii?
CANNOTANSWER.
How long did the treaty last?
A 7-year treaty was signed on January 30, 1875.
What happened after the 7 years ended?
At its expiration, 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 Treaty extended?