Read the passage carefully and answer the questions based on the passage:

Determination of Income and Employment

When, at a particular price level, aggregate demand for final goods equals aggregate supply of final goods, the final goods or product market reaches its equilibrium. Aggregate demand for final goods consists of ex ante consumption, ex ante investment, government spending etc. The rate of increase in ex ante consumption due to a unit increment in income is called marginal propensity to consume. For simplicity we assume a constant final goods price and constant rate of interest over short run to determine the level of aggregate demand for final goods in the economy. We also assume that the aggregate supply is perfectly elastic at this price. Under such circumstances, aggregate output is determined solely by the level of aggregate demand. This is known as effective demand principle. An increase in autonomous spending causes aggregate output of final goods to increase by a larger amount through the multiplier process. Full employment level of income is that level of income where all the factors of production are fully employed in the production process. The equilibrium attained at the point of equality of Y and AD by itself does not signify full employment of resources. Equilibrium only means that if left to itself the level of income in the economy will not change even when there is unemployment in the economy. The equilibrium level of output may be more or less than the full employment level of output.

What is the equilibrium output when autonomous investment increases from 10 to 20 at a given $C = 40 + 0.8Y$?

300

The correct answer is Option (2) → 300 

Given:

• Consumption function ($C$): $C=40+0.8Y$

• Investment increases from 10 to 20

AD=C+I.

Thus, AD=(40+0.8Y)+20 

         AD=60+0.8Y

At equilibrium, Y = AD.

                     Y=60+0.8Y

                     Y−0.8Y=60

                     0.2Y=60

                      Y =300​​