Table 10-3 Quantity Private Value Private Cost External Benefit $22 $11 $10 2 $20 $14 $10 3 $18 $17 $10 4 $16 $20 $10 5 $14 $23 $10 6 $12 $26 $10 Refer to Table 10-3. The socially optimal quantity of output is Select one: O a. 4 units. O b. 3 units. O c. 5 units. O d. 6 units