Liquid Solution

For a 1.0 molal solution containing the non-volatile solute Urea, the elevation in boiling point is 2.0 K while the depression in freezing point in a 3.0 molal solution having the same solvent is $4.0 K$. If the ratio $\frac{K_b}{K_f}=\frac{1}{X}$, what is the value of $X$ ?