Final concentration of NaOH?

Question

What is the final concentration of NaOH when 335 mL of .75 M NaOH are mixed with 165 mL of .15 M NaOH?

Please explain how you came with the answer

Answer 1

1. work out the moles in each (eg 335/1000 x 0.75)
2. add the two quantities of moles together
3. add the two volumes together, and convert it to litres.
4. divide 2 by 3.