A product has an average labor cost of $$\frac{10}{h}r.$ The overhead expenses are $100\%$ of labor cost. Time for the first unit$=10$ hours. Time for the fourth unit$=8\mathrm{.}1$ hours. Answer the following questions: $(10$ Points$)$

a$)$ Find the learning curve percentage for the production of this product.

b$)$ What is the labor cost and overhead cost for the $500-$th unit?