A body is dropped on ground from a height ' $\mathrm{h}_1$ ' and after hitting the ground, it rebounds to a height ' $\mathrm{h}_2$ ' If the ratio of velocities of the body just before and after hitting ground is 4 , then percentage loss in kinetic energy of the body is $\frac{x}{4}$. The value of $x$ is $\_\_\_\_$ .