Sam Owns a Candy Factory and Hires Workers in a Competitive

Sam owns a candy factory and hires workers in a competitive labor market to pack cases of candy. The company's weekly output of cases of candy varies with the number of workers hired, as shown in the following table:  
$$\begin{array} { | c | c | } \hline \begin{array} { c } \text { Number d } \\\text { warkers }\end{array} & \text { Cases/reek } \\\hline 0 & 0 \\\hline 1 & 160 \\\hline 2 & 310 \\\hline 3 & 450 \\\hline 4 & 580 \\\hline 5 & 700 \\\hline 6 & 810 \\\hline\end{array}$$  
If each case sells for $5 more than the cost of the materials used in producing it, then the value of marginal product of the 2?? worker is ________ per week.

A) $150
B) $310
C) $315
D) $750