Chemistry help: concentrations

I'm stuck on this question, so any help is welcome.

0.10 mol dm-3 of NaCl and 0.20 mol dm-3 of KCl solutions are used to make a mixture of the two solutions where NaCl has a concentration of 0.075 moldm-3 and KCl has a concentration of 0.05 moldm-3. what ratio of NaCl to KCl is added?

This might be super simple, but I just have no idea where to start.

Assume that your final solution has a volume of 1dm3 for simplicity.
The mol of each component in the final solution will be 0.075 and 0.05 respectively.
Now determine the volume of each stock solution that is needed to get this number of moles
= 0.75 dm³ and 0.25 dm³
Which is a ratio of 3:1