Could you please answer this question # 12 with explanation?

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QUESTION 12 The demand for toy cars is 10 each week. Every week, each unsold inventory will cost you $0.02. When you order the toy car from the supplier, the ordering cost is $2.5 each time. You decide to allow backorder and estimate the backorder cost to be $0.04 per unit. What is the maximum toy car inventory you have in store when you try to minimize the total cost