A video of a 12-year-old boy crying in frustration as his 9-year-old sister refuses to let him teach her math has gone viral on Chinese social media.

According to Chinese news outlets, the viral moment occurred on Oct. 11 in the siblings’ home in Anshan, China. Their mother, identified by her surname Zhong, posted the video of them online last week.

“I told her directly the answer that there are three right angles in this picture, but she still insisted that there are two right angles,” the boy reportedly says.

He eventually breaks down and can be seen holding onto a chair. His sister then starts crying as well.

“I’ve pointed out to her the three angles. She was so stubborn that she still said there are just two,” the boy laments.

While filming, Zhong jokingly tells her son, “You are also not qualified as a teacher.”

Zhong’s video, which has already received over eight million views on China’s Douyin, amused many of the social media platform’s users, with one writing, “I think the boy instantly aged 50 years.”

Back in June, a Chinese father went viral for a similar situation. He was filmed bursting into tears after his son, whom he tutored every day for a year, only received six out of 100 points on a math exam.

Featured Image via @吉视第一报道