Titration calculations

A 0.500 g sample of an impure sodium chloride solid is dissolved in water and made up to 250 cm$^3$. 25.0 cm$^3$ of this solution requires 22.5 cm$^3$ of 0.100 mol/dm$^3$ silver nitrate for complete precipitation of chloride ions.

$\text{Ag}^+ + \text{Cl}^- \rightarrow \text{AgCl}$

What is the percentage purity of sodium chloride in the solid? ($M_r$ of NaCl = 58.5)