Hyder Ali asked the rulers of Cochin and of Travancore to pay tribute as vassal states. Cochin was asked to pay a total of Rs. 400,000 and ten elephants, while Travancore was asked to pay Rs. 1,500,000 and thirty elephants. The Cochin royals agreed to pay the amount and accepted the Mysore's superiority. Finally, Malabar and Cochin came under the Mysore rule, opening Malabar Coast to the kings of Mysore.  However the King of Travancore, who was under the protection of the East India Company, refused to pay the tribute. Eventually the Mysore army began to move to Travancore from the north. The Dutch military garrison at Cranganore Fort tried to stall the movement. Hyder Ali asked his commander Sardar Khan to take an army of 10,000 along the Cochin Kingdom. In August 1776, Cochin was invaded from the north and the fort at Trichur was captured. After the surrender of the ruler of Cochin, Hyder advanced to the Travancore Defence Lines . By this time Airoor and Chetuva Fort were ceded to Mysore. Meanwhile, the Dutch, with the help of the Travancore Nair Army, put down an attempt by the Mysore forces to capture the Cranganore Fort. The ruler of Cranganore, however surrendered to Hyder Ali, though the Dutch stormed his palace and captured it in January 1778.

Based on the above article, answer a question. How many years was it from when the fort at Trichur was captured until when the ruler of Craganore surrendered to Hyder Ali?
2