A−B means ‘A is the wife of B’;
A+B means ‘A is the sister of B’ and
A∗B means ‘A is the father of B’.

If Q−T∗Y+M−K, then how is Q related to K?

Let's decode the given expression from left to right:
Q−T: Q is the wife of T. (⟹T is the husband/male, Q is female).

T∗Y: T is the father of Y.

Y+M: Y is the sister of M.

Since T is the father of Y, T is also the father of M. Consequently, Q is the mother of both Y and M.

M−K: M is the wife of K. (⟹M is female, K is her husband).

Now, let's find how Q is related to K:

M is the daughter of Q.

K is married to M (so K is the son-in-law of Q).

Therefore, Q is the Mother-in-law of K.

Hence, the correct option is A.