Answer:
Consumption c is a function of disposable income
Investment I is a function of interest rate
Marginal propensity to consume equals 0.8
If this 3, I = investment
= 500-(3*50)
= 500-150
= 350
We have Y= C+I+G
Y = 120+0.8(Y-125)+350+150
Y = 120+0.8Y-100+350+150
Y-0.8Y = 120-100+350+150
0.2Y = 520
Y = 520/0.2
Y = 2600
GDP and interest rate falls below full employment
If there is no change in monetary policy an increase in government purchases by 50dollars takes gdp back to full employment
If no change in fiscal policy when interest rate decreases by 1.4% God goes back to full employment.