8. (3 points) The expenditure of a household on consumer goods, C, is related to the household's income, :9, in the following way: When the household's income is $1000, the expenditure on consumer goods is $900, and whenever income increases by $100, the expenditure on consumer goods increases by $80. Express the expenditure on consumer goods as a function of income, assuming a linear relationship, and sketch the graph with C as the horizontal axis and y as the vertical axis