What would be the calculated value for the percentage of KClO3 in the mixture if....?

A student obtained the following data in this experiment: m of mixture= 1.500g, barometric pressure= 760.0 torr, volume of water displaced= 250.0mL, and a temperature of the gas = 25.0C. If the student's calculated value for R is 50.0 L-torr/mol-K, what would be his calculated value for the percentage of KClO3 in the mixture?