Two identical spheres each of mass \( 2 \, \text{kg} \) and radius \( 50 \, \text{cm} \) are fixed at the ends of a light rod so that the separation between the centres is \( 150 \, \text{cm} \). then, moment of inertia of the system about an axis perpendicular to the rod and passing through its middle point is \( \dfrac{x}{20} \, \text{kg m}^2 \) , where the value of \( x \) is ________.
