Stearic acid (C₁₈H₃₆O₂) and palmitic acid (C₁₆H₃₂O₂) are common fatty acids. Commercial grades of stearic acid usually contain palmitic acid as well. A 1.115 g sample of a commercial-grade stearic acid is dissolved in 50.00 mL benzene (d = 0.879 g/mL). The freezing point of the solution is found to be 5.072 °C. The freezing point of pure benzene is 5.533 °C, and K_f for benzene is 5.12 °C kg mol^-1. What is the mass percent of palmitic acid in the stearic acid sample?