A product that is very labor intensive assembled at Boyds Aero Structure in Memphis has an average labor cost of $$\frac{20}{h}r.$ Overhead expenses are charged at $100\%$ of labor at this company.

Time for the very first unit $=10$ hours

Time for the fourth unit $=8\mathrm{.}1$ hours.

What is the cumulative time in hours for $100$ units to be made?