An economy is described of the following equations:

C=1800+0.6(Y-T)

I=900

G=1500

NX=100

T=1500

Y*=9000

a) Find an equation linking aggregate demand to output.

b) Find autonomous aggregate demand and induced aggregate demand.

c) What is the output gap?

d) What happens to the equilibrium if autonomous aggregate demand increase by $20.

Recalculate the output gap.