Question

calculate the molality, molarity, and mole fraction of NH3 in an 12.80 mass % aqueous solution (d=0.9651 g/ml)

Answer 1

mass % is grams solute/100 g solution.

12.8% w/w is 12.8g NH3/100 g solution.
mass = density x volume. You know 100 g solution and density of the solution; solve for volume of the solution.
Convert g NH3 to mols NH3. g/molar mass = mols.
Then M = mols/L solution.
m = mols solute (same as for M)/kg solvent.
To do mol fraction, convert g NH3 to mols which you did above.'
Convert g H2O to mols.
Then XNH3 = mols NH3/total mols.