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This post uses English words incorrectly, and, in addition, it is uncompleted.
(1) a store, as usual, does not produce items: it them, instead.
(2) are these 20 cents per pack the price to buy a pack from outside or to sell it ?
(3) the problem never say at which price it sells the packs.
Formulated in this way, the problem CAN NOT be solved correctly.
Be careful formulating your problems.
It is Math, where each word does matter.