The figure below shows the demand and supply curves in the market for elementary education.Figure 13.1
In the figure,
D: Private demand curve for elementary education
D + s: Demand curve which includes public benefits
S: Supply curve of education
Price and Quantity have been taken on vertical and horizontal axes respectively.
-According to figure 13.1, the optimal subsidy is equal to:

Question

The figure below shows the demand and supply curves in the market for elementary education.Figure 13.1
In the figure,
D: Private demand curve for elementary education
D + s: Demand curve which includes public benefits
S: Supply curve of education
Price and Quantity have been taken on vertical and horizontal axes respectively. 
-According to figure 13.1, the optimal subsidy is equal to:

Quizplus · Accepted Answer

The optimal subsidy is the difference between the private demand and the supply curves at the socially optimal quantity (where D+s intersects with S). In the figure, this quantity is represented by point b where D+s intersects with S. Therefore, the optimal subsidy is equal to the distance between point b and the supply curve S, which is represented by the vertical distance between points b and d. This distance is given by Q_sb - Q_sd. Therefore, the correct answer is D.

The Figure Below Shows the Demand and Supply Curves in the Market