How to get Item cost Calculated for Parent Item without using Manufacturing?

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I have a case that we have many Parent item for example item 1 and this item has two child item which get procured RM1 and RM2, and we are using perpetual costing, so i defined Item structure for Item 1, having RM1 and RM2 as child items in the structure, i have cost for RM1 and RM2 bas on PO Receipts, but how i can get cost for Item 1?

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