2.2. At the beginning of January 2019, Borya and Vitya started saving money for a new phone. On the 20th of each month, Borya saved 150 rubles, and Vitya saved 100 rubles. One day, Vitya got tired of saving money and stopped saving (but he did not spend the money he had already saved). Borya continued to save. On May 11, 2021, Borya's savings were 7 times greater than Vitya's. In which month did Vitya stop saving? Specify the month and year.
Answer: July, 2019

Solution. By May 2021, Borya will have been saving for 28 months, that is, he will have set aside $28 \cdot 150=$ 4200 rubles. This means Vitya saved $4200: 7=600$ rubles, that is, he saved for a total of 6 months. This means that in June he was still saving money, but in July he was not.