NEED HELP WITH QUESTION $4.$ I GAVE THE CORRECT ANSWERS FOR $1-3$ FOR CONTEXT

A bakery buys flour from its supplier at a price of $$1/$lb and uses it to produce a variety of baked goods. The inventory holding cost is $20\%$ of the price of the flour per year. Each order placed with the supplier costs the bakery $$10$ in fixed overhead costs, irrespective of the order amount. Suppose the bakery uses flour at a constant rate of $50$ lbs$/$week and there are $50$ weeks in a year.

$1.$ How much flour $($in lbs$)$ should the bakery purchase in each order to minimize the total ordering and holding cost in a year? If your answer is not an integer, provide at least three decimal places, e$.$g$.,7\mathrm{.}500.$ CORRECT ANSWER: $500$

$2.$ If the bakery orders the amount you calculated in Question $1,$ how many orders should they place in a year? If your answer is not an integer, provide at least three decimal places, e$.$g$.,7\mathrm{.}500.$ CORRECT ANSWER: $5$

$3.$ If the bakery orders the amount you calculated in Question $1,$ what is the total yearly ordering and inventory holding cost? If your answer is not an integer, provide at least three decimal places, e$.$g$.,7\mathrm{.}500.$ CORRECT ANSWER: $100$

$4.$ The supplier is running a special offer: if the bakery purchases $1000$ lbs in an order, they get $$10$ cashback. What is the bakery's NET yearly ordering and inventory holding cost if they avail this offer? If your answer is not an integer, provide at least three decimal places, e$.$g$.,7\mathrm{.}500.$

Hint: You need to calculate the total yearly ordering and inventory holding cost and the number of orders placed in a year under this new order quantity. The NET cost $=$ the total cost $-$ total cashback received in a year.