The number of orders in is equal to the number of orders out in month 4 (April). It appears the solution represents the time at which warehouse shipments caught up with order quantities.
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For this table to make any sense, we have to assume that the year started with 3 orders in January, and that one order was shipped in January. Then the number of orders was 1 or 2 each month after that, and the number of orders shipped per month was 2 each month after that. That is, the tables represent year-to-date totals of orders in and out.
<em>Alternate Interpretation</em>
If the numbers here are actual orders in and out in each of the listed months, it appears the warehouse is getting better at shipping orders. That is, they are increasing the shipment rate by 2 orders a month each month. They will eventually ship enough to cover the total number of orders in (total of 20 by April), but total shipments through April only amount to 16 orders.
