250-g sample of a magnesium-aluminum alloy dissolves completely in an excess of HCl (aq). When the liberated H2 (g) is collected over water at 29 and...

A 0.250-g sample of a magnesium-aluminum alloy dissolves completely in an excess of HCl (aq). When the liberated H2 (g) is collected over water at 29 and 752 torr, the volume is found to be 317 mL. The vapor pressure of water at 29 degrees C is 30 torr. What is the mass percentage of aluminum in this alloy?