Calculate the molar mass of the unknown density of acetone

Question

What will be the boiling point of a solution of 20.0 g of urea ((NH₂)₂CO) in 1.25 kg of nitrobenzene (use Table 8.2).
2. A 1.89 g pellet of an unknown compound was dissolved to 50 mL of acetone. The change in the boiling point was found to be 0.64 °C. Calculate the molar mass of the unknown. Density of acetone is 0.7851 g/mL and the value of ebullioscopic constant Kb may be found in Table 8.2.