How much to list for quantity and variation?

Hello everyone, I would like to ask for some clarification. I have a total of 6 items of the same style (dress), within the 6 total, I have 2 items of each size. So, 2 small, 2 medium, 2 large. Would I list 6 or 2 as the quantity under “product offer?”

If I list 6 items as the total quantity, where can I go to list that I have 2 items available in each size?

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Thank you, all.