Which accounting principle states that a company should "report expenses in the same period as the revenue they generate"?

In june, one of the processinthe assembly department started the month with 25,000 units in its beginning work in process inventory. an additional 310,000 units were transferred in from the prior department during the month to begin processing in the assembly department. there were 30,000 units completed and transferred to the next processing department during the month. how many units the assembly department started the month with 25,000 units in its beginning work in process inventory. an additional 310,000 units were transferred in from the prior department during the month to begin processing in the assembly department. there were 30,000 units completed and transferred to the next processing department during the month. how many units were in its ending work in process inventory