5. Ch. 4 By using REPEATED SUBSTITUTION method only, please answer the following Macroeconomics question: Consider the simplified, two-equation, national income model Y =C+I C = a + by Where national income (Y) and consumption (C) are endogenous variables and investment (/) are exogenous variables. The parameters in the consumption function, where a represent the autonomous consumption expenditure and b represents the marginal propensity to consume, respectively