After dinner, Xue Erfu asked the two children, "Xue Yan, Jiang Yue, when are you going to sleep? If you're not in a hurry to sleep, teach me how to read the account book."
Jiang Yue and Xue Yan were not in a hurry to sleep. They were also willing to teach Erfu, so they naturally agreed. Then, they walked to the counter and patiently taught Erfu to read the account book.
The account book was easy to read, but there were some words on it that Erfu did not recognize, so he could not understand some parts of it.
They then taught Erfu how to read the words he could not recognize.
Erfu also understood that it was not that the account book was difficult, but that he was too illiterate. He even quickly took out a pen and paper for notes while recognizing it to make a deeper impression.
Just as he was teaching Erfu, someone knocked on the door of their shop.