Refer to the Following Table That Gives the Demand Facing $$\begin{array} { c c } \text { Price } & \text { Quartity } \\\hline \$ 20 & 20 \\15 & 40 \\10 & 55 \\5 & 70\end{array}$$

Refer to the following table that gives the demand facing a monopolist:
$$\begin{array} { c c } \text { Price } & \text { Quartity } \\\hline \$ 20 & 20 \\15 & 40 \\10 & 55 \\5 & 70\end{array}$$
-How much does the 28th unit of output add to total revenue?

A) $2
B) $10
C) $20
D) $200
E) none of the above