Problem
My sister is a teacher in the university that I am enrolled in. During the exam, my best friend told me that a leakage of my sister's final exam is circulating online. My best friend told me not to tell my sister because she (my best friend) is failing my sister's class and she needs the leakage to pass the final exam.
I respect my sister, but I also do not want to betray my best friend. What should I do?