How Much Are Additional Units of Labor Worth Based on the Following

How much are additional units of labor worth based on the following sensitivity report?
$\text { Changing Cells }$
$\begin{array}{llrr}&&\text { Final}& \text {Reduced }\\\text { Cell } & \text { Name } & \text { Value } & \text { Gradient } \\\hline \$ B \$ 4 & \text { Number to make: } \mathrm{X}_{1} & 4 & 0 \\\$ \mathrm{C} \$ 4 & \text { Number to make: } \mathrm{X}_{2} & 8.571 & 0\end{array}$

$\text { Constraints }$
$\begin{array}{llrr}&&\text { Final }&\text { Lagrange}\\\text { Cell } & \text { Name } & \text { Value } & \text { Multiplier } \\\hline \$ \mathrm{D} \$ 8 & \text {Wood } & 84 & 0.714 \\\$ \mathrm{D} \$ 9 & \text { Labor } & 4 & 3.714 \\\$ \mathrm{D} \$ 10 & \text { Hinges } & 8.571 & 0\end{array}$