Sarah was born in the year 1993. Here's the calculation: - In 2023, Sarah is celebrating her 30th birthday - She has a younger sister who is 5 years younger than Sarah - The sister was studying abroad and couldn't attend the birthday party Therefore, Sarah must have been born in the year 1993 (2023 - 30 years = 1993). To confirm, if Sarah was born in 1993 and turned 30 in 2023, that lines up with the information given about the sister being 5 years younger and studying abroad on the day of Sarah's birthday party. The key pieces of evidence are Sarah's age at the birthday (30 years old), the age difference between the sisters (5 years), and the sister's absence due to being abroad, which allows us to calculate the birth year. The year Sarah was born is 1993. Returning only the four-digit year number.