Step 1: A is R's brother. A and R are siblings; A is male.
Step 2: C is B's mother. C is a parent of B; C is female.
Step 3: M is C's sister. M and C are siblings; M is female.
Final Relationship: M is the sister of B's mother (C). Therefore, M is B’s maternal aunt.
Correct Answer: Option 3 – Aunt
M is C's sister, and C is B's mother. This establishes M as B's maternal aunt. Consequently, M is B's aunt.