(a) Suppose that the macroeconomic-model of an economy is given as follows Consumption function: Y= 80+ 0.7Yd Investment function: I= 100+0.2Y Government spending: G= 160 Tax function: T= 60 + 0.15Y Transfer Payments: TR= 40 Transactions and precautionary demand for money: M*=0.25Y Speculative demand for money: MEP=280- 202r Nominal supply of money: M= = 2250 Price level: P= 4 (i) What is the general mathematical definition of the IS curve? (ii) Derive the equation that describes the IS curve