Percent Purity From Gas Collection

A 0.500 g sample of impure KClO₃ is heated, causing it to decompose according to the reaction: $2\mathrm{KClO}_3(s) \rightarrow 2\mathrm{KCl}(s) + 3\mathrm{O}_2(g)$. The resulting O₂ gas is collected over water at 25°C and a total pressure of 755 mmHg, occupying a volume of 95.0 mL. If the vapor pressure of water at 25°C is 23.8 mmHg, what is the percent purity of the KClO₃ sample?