4. Calculations with the IS curve: Suppose the parameters of the IS curve are a = 0, b = 0.5, 7 = 5% and the real interest rate is initially R =5%. Explain what happens to short-run output in each of the following scenarios ( consider each separately): (a) The real interest rate rises from 5% to 7%. (b) The real interest rate falls from 5% to 2%. Ill:(c) de decreases by 3 percentage point. (d) dam increases by 3 percentage points