I have data in this format, I want to know what is the diff of quantity between warehouse and the store, storewise

Warehouse
ItemId ItemDesc StoreId Qnty
i101 ItemA str21 9
i201 itemB str21 8
i101 ItemA str25 7
i201 itemB str25 9

Store
ItemId StoreId Qnty
i101 str21 5
i101 str25 3
i201 str21 2
i201 str25 3

Thanks in advance...