A nonvolatile organic compound Z was used to make up two solutions, Solution A contains 5.00 g of Z dissolved in 100 g of water, and Solution B contains 2.31 g of Z dissolved in 100 g of benzene. Solution A has a vapor pressure of 754.5 mmHg at the normal boiling point of water, and Solution B has the same vapor pressure at the normal boiling point of benzene. Calculate the molar mass of Z in solutions A and B and account for the difference.