Five$-$gallon i$.$e $128$ ounces stainless steel containers are filled with soft drink syrup on an automatic machine. The filling process is monitored by X$$ and R charts, based on samples of size six. These charts indicate that the process is in control, and the center line of the R chart is $0\mathrm{.}20$ fluid ounces. The filled containers are inspected, and all underfilled container are rejected. A container is sold for $$10$; however, an underfilled container must be refilled to correct volume. The additional labor cost associated with this refilling operation is $$2.$ The product cost is $$0\mathrm{.}10$ per fluid ounce. What is the optimum mean target level for the filling machine?