What mass of NaCl must be dissolved in 65.0 grams of water to lower the freezing point by 7.50 C?

What mass of NaCl must be dissolved in 65.0 grams of water to lower the freezing point by 7.50 °C? The freezing point depression constant, Kfp, for water is -1.86 °C/m. Assume the van't Hoff factor for NaCl is 1.87.