JEE Main PAPER - 1

A solid sphere of radius $r$   made of a soft material of bulk modulus $K$   is surrounded by a liquid in a cylindrical container. A massless piston of area $a$   floats on the surface of the liquid, covering entire cross section of cylindrical container. When a mass $m$   is placed on the surface of the piston to compress the liquid, the fractional decrement in the radius of the sphere, $\left(\frac{dr}{r}\right)$  , is: