The annual average income y of an American man

The annual average income y of an American man with an associate’s degree is given by the linear equation y = 1983x + 42,972, where x is the number of years after 1999. What does the slope of the equation represent? (Source: Based on data from U.S. Bureau of the Census, 1999­-2004). A. The average annual income of an American man with an associate’s degree in 1983. B. The number of years since 1999 that the average man with an associate’s degree had income. C. The increase in the average annual income of an American man with an associate’s degree each year. D. The average annual income of an American man with an associate’s degree in 1999.