P's father Q is B's paternal uncle and A's husband M is P's paternal uncle. How is A related to B ?

Explanation:-

Q is the paternal uncle of B, means Q is the brother of P's father. P is the son of Q. So, B's father and P's father are brothers.
Also, M is the paternal uncle of P, means M is the brother of P's father. So, M is the father of B. Since A is the wife of M, so A is the mother of B.