In decipher jumbled up description type of questions, a round-about description is given in the form of certain small relationships and direct relationship between the persons concerned is to be deciphered.
A man said to a lady, " Your mother's husband's sister is my aunt."
How is the lady related to the man ?
Your's mother's husband -- Your father ;
Your father's sister -- Your aunt.
So, lady's aunt is man's aunt and therefore lady is man's sister.