The elevation of boiling point of 0.10 m aqueous $\mathrm{CrCl}_3 . \mathrm{xNH}_3$ solution is two times that of 0.05 m aqueous $\mathrm{CaCl}_2$ solution. The value of x is $\_\_\_\_$ . [Assume $100 \%$ ionisation of the complex and $\mathrm{CaCl}_2$, coordination number of Cr as 6 , and that all $\mathrm{NH}_3$ molecules are present inside the coordination sphere]