The solubility is the guide to the maximum amount of solute that can be dissolved in a certain amount of solvent at a certain temperature to make a saturated solution. Any amount less than this would result to unsaturated, while any amount more would result to saturated.
6 g/(50 mL * 1 L/1000 mL) = 120 g/L
Since it is less than the solubility of 125 g/L, then this solution is unsaturated.