[doug_martin]

A 0.03146 g sample of a mixture of NaCl and KBr was dissolved in water.  The resulting solution required 35.30 ml of 0.08765M AgNO3 to precipitate the Cl- and Br- as AgCl and AgBr.   
Calculate the mass percentage of NaCl in the mixture.

I calculated the millimoles of AgNo3 as 3.094, but am unsure where to go from here.    I need to understand the problem - I do not think we have enough info to do the problem.    What am I missing?

[Borek]

You can write two equations describing the system. One will use info about sum of masses, the other about sum of moles.

[doug_martin]

Huh - I must be brain dead - I am still missing something here.

[Borek]

Try to write these equations. Assume there are m_NaCl and m_KCl in the sample.