Table 10-3
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​ -Refer to Table 10-3

Table 10-3
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$$\begin{array} { | c | c | c | c | } \hline \begin{array} { c } \text { Quantity } \\\text { (Units) }\end{array} & \begin{array} { c } \text { Private Value } \\\text { (Dollars) }\end{array} & \begin{array} { c } \text { Private Cost } \\\text { (Dollars) }\end{array} & \begin{array} { c } \text { External Benefit } \\\text { (Dollars) }\end{array} \\\hline 1 & 22 & 12 & 10 \\\hline 2 & 20 & 15 & 10 \\\hline 3 & 18 & 18 & 10 \\\hline 4 & 16 & 21 & 10 \\\hline 5 & 14 & 24 & 10 \\\hline 6 & 12 & 27 & 10 \\\hline\end{array}$$
-Refer to Table 10-3. The socially optimal quantity of output is

A) 3 units.
B) 4 units.
C) 5 units.
D) 6 units.