Determine the molality of an aqueous solution that is 16.5 percent urea by mass

Take a hypothetical sample of exactly 100 grams of the solution.

(16g urea) / (60.06 g urea/mol) = 0.2664 mol urea

((100 g total) - (16g urea)) = 84.0 g H2O = 0.0840 kg H2O

(0.2664 mol) / 0.0840 (kg) = 3.17143mol/kg = 3.18m urea