Answer: The volume of the balloon at this altitude is 46.3 L
Step-by-step explanation:
Combined gas law is the combination of Boyle's law, Charles's law and Gay-Lussac's law
The combined gas equation is,

where,
= initial pressure of gas = 755 mm Hg
= final pressure of gas (at STP) = 385 mm Hg
= initial volume of gas = 27.6 L
= final volume of gas = ?
= initial temperature of gas =

= final temperature of gas =

Putting all the values we get:


Thus the volume of the balloon at this altitude is 46.3 L