molality is defined as the number of moles of solute in 1 kg of solvent.
since density and volume has been given we can calculate the mass of water
mass = density x volume
mass = 1.00 g/mL x 1620 mL = 1620 g
number of moles of glucose - 257 g / 180 g/mol = 1.43 mol
number of moles of glucose in 1620 g - 1.43 mol
therefore number of moles in 1000 g - 1.43 mol / 1.620 kg = 0.883 mol/kg
therefore molality is 0.883 mol/kg
