Answer : The volume of the bubble is, 625 mL
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 = 2.4 atm
 = initial pressure of gas = 2.4 atm
 = final pressure of gas = 1.0 atm
 = final pressure of gas = 1.0 atm
 = initial volume of gas = 250 mL
 = initial volume of gas = 250 mL
 = final volume of gas = ?
 = final volume of gas = ?
 = initial temperature of gas =
 = initial temperature of gas = 
 = final temperature of gas =
 = final temperature of gas = 
Now put all the given values in the above equation, we get:


Therefore, the volume of the bubble is, 625 mL