15. A circular disc X of radius R is made from an iron plate of thickness t, and another disc Y of radius 4R is made from an iron plate of thickness

A circular disc X of radius R is made from an iron plate of thickness t, and another disc Y of radius 4R is made from an iron plate of thickness t/4 .  Then the relation between the moment of inertia I_X and I_Y is

(a)  I_Y = 64I_X

(b)  I_Y = 32I_X                                     

(c)   I_Y = 16I_X

(d)  I_Y = I_X

Ans. a