A simple Macro model. In a closed economy (no trade), the government does three things. It purchases goods and services

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A simple Macro model.
In a closed economy (no trade), the government does three
things. It purchases goods and services (G), it collects tax
revenue (T) and it makes transfers to household and businesses
(TR).
G = 50
T = 20 + 0.2 × Y
T R = 10 − 0.1 × Y
where Y is national income.
The basic consumption function is given by
C = 30 + 0.8 × YD
where YD is disposable national
income.
The desired investment is an autonomous term
I = 30
a) Write down the equation for the AE (aggregate expenditure)
function for this economy.
b) Compute the equilibrium level of national income in this
economy.
c) Compute the value of the simple multiplier.