The solubility of NaCl in water at 100 C is 40%, meaning that we can dissolve 40 g NaCl in 100 g water. Assuming that dissolving NaCl does not add any volume to the solution, 600 mL of water is approximately equal to 600 g of water. By ratio and proportion: 40 g NaCl/100 g H2O = x g NaCl/600 g H2O
x = 240 g NaCl
So 240 g of NaCl must be dissolved to form a saturated solution.