-What Is the Marginal Cost for the 5th Unit of }

$\begin{array}{cccccc}\text { Level of } & \text { Total } & \text { Total } & \text { Marginal } & \text { Marginal } & \text { Net } \\\text { Activit } & \text { Beneft } & \text { Cost } & \text { Benefit } & \text { Cost } & \text { Benefit }\\\hline0&-&0&xx&xx&0\\1&100&50&-&-&-\\2&-&-&150&0&100\\3&-&-&-&160&115\\4&605&-&-&179&-\\5&-&674&120&-&-\\6&825&-&-&190&-\end{array}$
-What is the marginal cost for the 5th unit of the activity?

A) 180
B) 175
C) 189
D) 186
E) none of the above