I had the exact same doubt, but since a similar question was discussed in my class, and sir gave as modulus ka square, I assumed the same.
Imagine a regular hexagon as given. Put six unit masses on the vertices, one on each. Calculate total moment of inertia about the centre. Since the moduli of the complex numbers is same, and mass kept is 1, what you’ll get is the sum of square of the moduli.
P.S you should wait for the others to come up with a more math like solution