The normal boiling point of a certain liquid $x$ is $138\mathrm{.}5C,$ but when $71.\mathrm{.}9g$ of urea $,(($NH$2)2)$CO$)$ are dissolved in $700$ of $x,$ it is found that the solution boils at $140\mathrm{.}6C$ instead Use this information to calculate the molal boiling point elevation constant $K_b$ of $x.$

Be sure your answer has the correct number of significant digits