I sell goods and buy other goods with the profits, so how do I pay zakah?

Question:
He says: Honorable Shaykh, may Allah grant you success. He says: I have goods and I sell them, but I always invest the profits resulting from the sale to buy other goods. His question is: How do I pay zakah? Knowing that I have not taken the profits?

Answer:
If a lunar year has passed on the capital with which you sell, and a lunar year has passed on the capital, you appraise the goods you have on display for sale. You appraise them at their value, or what they are worth, and you pay zakah on them by giving one-quarter of a tenth. Yes.