The unit "m" in this given is used to refer to molality which is equal to the number of moles of the solute divided by the mass in kg of the solvent. If we let x be the mass of iodine, the equation for molality then becomes,
molality = (x / 253.8) / ((950 mL)(1.594 g/mL)(1 kg/ 1000 kg)
0.75 = (x / 253.8) / 1.5143
The value of x 288.247 g
Answer: 288.25 g