$$I_{X Y}=I_{C M}+M R^2=\frac{2}{5} M R^2+M R^2=\frac{7}{5} M R^2=\frac{7}{5} \times 5 R^2=7 R^2\quad \text{.... (1)}$$

$$\begin{aligned} & I_{X Y}=M K^2=5 \times 5^2 \quad \ldots(2) \\ & \therefore 5 \times 5^2=7 \times R^2 \quad \text { [From (1) and (2)] } \\ & \Rightarrow R=\sqrt{\frac{5}{7}} \times 5=\frac{5 x}{\sqrt{7}} \quad \text { (Given) } \\ & \therefore x=\sqrt{5} \end{aligned}$$