2. Consider the economy described in chapter 3 (a closed economy, the factors of produc- tion are in fixed supply and fully used, prices adjust to balance supply and demand, etc). Consumption is a linear function of disposable income and the marginal propen- sity to consume is 0.6. The investment function is: / = 100-80r (where / is investment and r is the real interest rate). (a) Explain how an increase in output (due to technological progress) affects the equilibrium interest rate. (b) Calculate the change in the equilibrium interest rate if technological progress increases output by 5 units