70,000 yen is the sum of only the November shipments (30,000 on 11/6 plus 40,000 on 11/15). The shipment of 20,000 yen on 10/30 took place after the billing on 10/21, so it has not been billed yet and must be included in the 11/21 billing. This error arises from thinking that only shipments in the same month as the billing count.
○イ
正解Billing is based on the shipped data, with a cut-off on the 20th of each month and the invoice prepared on the following day, the 21st (outline of operations (3)). Therefore, billing e on 11/21 includes only what was actually shipped after the previous billing on 10/21 and up to the 11/20 cut-off. Following the shipment rows in the table, the shipment of 20,000 yen on 10/30, 30,000 yen on 11/6, and 40,000 yen on 11/15 fall in this period, totaling 20,000＋30,000＋40,000＝90,000 yen. The shipment of 35,000 yen on 11/25 is recorded in the table after the 11/21 billing row and is past the cut-off date, so it is carried over to the next billing (12/21). Also keep in mind that an order received is only a record that an order was taken; it does not become subject to billing until the shipment is completed. Therefore the correct answer is イ, 90,000 yen.
×Incorrectウ
105,000 yen is the sum of 30,000 on 11/6, 40,000 on 11/15, and 35,000 on 11/25. The 11/25 shipment is past the 20th cut-off and, in the table as well, is recorded after the 11/21 billing row, so it is not included in this billing. In addition, it wrongly leaves out the 10/30 shipment.
×Incorrectエ
155,000 yen is the sum of the four orders received after the previous billing on 10/21 (30,000 on 11/3, 40,000 on 11/5, 35,000 on 11/10, and 50,000 on 11/20); it is the error of totaling on an order-received basis. Billing processing is performed based on the shipped data, so amounts that have only been ordered and not yet shipped must not be billed.
ここがポイント
Billing processing is based on the shipped data. An order received (a record that an order was taken) is not subject to billing; you can bill only after the shipment has been completed.
The relationship between the cut-off date and the billing date: if the cut-off is the 20th of each month and billing is on the 21st, the target is the shipments made after the previous billing and up to the current cut-off date, while shipments after the cut-off date are carried over to the next billing.