Question $6,7,8,9$ and $10$ are about the following problem $($similar to the one in my video lecture$)$

Clarissa Seager is the purchasing agent for Central Valve Company, which sells industrial valves and fluid$-$control devices. One of its most popular valves is the Western, which has an annual demand of $4,000$ units. The cost of each valve is $$90\mathrm{.}00,$ and the inventory carrying cost is estimated to be $10\%$ of the cost of each valve. Clarissa has made a study of the costs involved in placing an order for any of the valves that Central Valve stocks, and she has concluded that the average ordering cost is $$25\mathrm{.}00$ per order. Furthermore, it takes about $8$ work days for an order to arrive from the supplier. During this time, the demand per week $(=5$ work days$)$ for Central's valves is approximately $80.$ Assume there are $250$ work days per year.

What is the optimal number of orders per year? Round the number up to the nearest unit