In an electric circuit, a call of certain emf provides a potential difference of 1.25 V across a load resistance of $5 \Omega$. However, it provides a potential difference of 1 V across a load resistance of $2 \Omega$. The emf of the cell is given by $\frac{x}{10} \mathrm{~V}$. Then the value of $x$ is $\_\_\_\_$ .