ysis of a Magnesium-Aluminum Alloy?

A 0.250-g sample of a magnesium-aluminum alloy dissolves completely in an excess of HCl (aq). When the liberated H2 is collected over water at 29 C and 752 torr, the volume is found to be 311 mL. The vapor pressure of water at 29 C is 30.0 torr. What is the m percentage of aluminum in this alloy?