Answer : The initial temperature of gas would be, 269.7 K
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 = 0.723 atm
= final pressure of gas = 0.612 atm
= initial volume of gas = 13.5 L
= final volume of gas = 17.8 L
= initial temperature of gas = ?
= final temperature of gas = 
Now put all the given values in the above equation, we get:


Thus, the initial temperature of gas would be, 269.7 K