Question

Calculate the molality of acetone in an aqueous solution with a mole fraction for acetone of 0.235. Answer in units of m.

Answer 1

acetone = Ac2O

I would try something like this.
Take some value of g H2O, say 18 g (you may need to use more precise numbers than I).
moles H2O = 18/18 = 1 mole.
Then X_H2O = 0.765 = (1 mole H2O/1 mole H2O + x moles Ac2O).
Solve for x moles Ac2O. Convert mols Ac2O to grams Ac2O remembering g = mols x molar mass.

Now you have grams water and mole Ac2O, molality = moles/kg solvent.
Post your work if you get stuck.