Consider an economy with the following characteristics: Consumption function is C = 100 + 0.8YD; Planned investment: I = 50; Government expenditure: G = 60; The tax function: T = 0.3Y; Exports of the country: X = 20 The import function: M = 10 + 0.06Y. Assume there are no transfer payments and no autonomous taxes. All variables are in billions of dollars. C is consumption expenditure; YD is disposable income; Y is real GDP; G is government purchases of goods and services; T is taxes; I is planned investment expenditure; X is exports, and M is imports. 3 a. Write the aggregate expenditure function and find out the value of equilibrium level of income of the economy b. What is the value of consumption expenditure of the economy? c. Define the concept of multiplier. Calculate the size of the multiplier of the economy if government expenditure rises from $60 billion to $100 billion. Does the open economy multiplier is bigger than closed economy multiplier?

(please don't use others AI to answer this question and I am more concerned to find 3c. which formula is directly to use according to the this case? is it 1/1-(mpc) or 1/1-(mpc+mpm) or 1/1-(mpc+mpm+mpt) ? and can you please explain why are you using that formula?

2. Gross fixed capital formation (GFCF) (investment) one of the most volatile components of GDP. In a diagram, show the movement of private and public GFCF of Australia over 2005 and 2024.(diagram graph). Explain why GFCF is an important contributor to an economy.