Complex sentence: When his uncle, Simon McTavish, visited from Montreal in 1776, he paid for William's education and in 1784 his uncle brought him out to Canada to work for him in the North West Company, with an annual salary of £100 per year.
Split into simpler sentences: When his uncle, Simon McTavish, visited from Montreal in 1776, he paid for William's education. On completing this education, in 1784 his uncle brought him out to Canada to work for him in the North West Company, with an annual salary of £100 per year.