In 1714, Peter the Great sent a party of shipbuilders to Okhotsk to allow faster access to the furs of Kamchatka. In 1715, they built the Vostok and in 1716–17 Kozma Sokolov sailed it to Kamchatka. For the next 145 years Okhotsk was the main Russian seaport on the Pacific, supplying Kamchatka and other coastal settlements. In 1731 the Siberian Military Flotilla was established here. In 1736, Okhotsk was moved two miles downstream to a spit of land at the mouth of the Okhota, converting the ostrog (fortress) into a proper port. Vitus Berings two Pacific expeditions (1725–1729 and 1733–1742) brought in large numbers of people and the first scholars and expert sailors and led to a great deal of building. In 1742 there were 57 buildings, 45 other buildings in the Berings "expedition settlement" and eight ships in the harbor. Anton de Vieira, of Portuguese people origin (son of a Jewish father and Christian mother), was the towns governor at that time. From 1737 to 1837 there was a salt works several miles west on the coast that produced 14–36 tons annually. In 1827 it was worked by 150 exiles and about 100 guards and overseers.
Question: How many years before the end of the salt works was it worked by 150 exiles and 100 guards and overseers?
Answer: 10