If 3.0 liters of 0.50 m nacl (aq) is mixed with 9.0 liters of 0.2777 m nacl (aq), what is the final concentration of the resulting solution?

First, we shall calculate the total number of moles present in the final solution.
Number of moles in 0.50 m NaCl = molarity * volume = 0.50 * 3.0 = 1.5 moles.
Number of moles in 0.2777m NaCl = molarity * volume = 0.2777 * 9.0 = 0.24993 moles
Total number of moles = 1.5 + 0.24993 = 1.74993 moles

Second, we shall calculate the total volume of the final solution.
Total volume = 3 + 9 = 12 litres.

The molarity = total number of moles / total volume = 1.74993 / 12 = 0.1458 m