VTMO 2026 - Grade 7 - Semifinal - SET 9 - Self-study Question 13

Vinh takes 75 minutes to travel from $A$ to $B$, while Quang takes 60 minutes. Vinh leaves 9 minutes before Quang. When Quang catches Vinh, they are still 12 km from $B$. How long is $AB$, in km?