76.6 litres is the volume of the gas if pressure and temperature changes to STP.
Explanation:
Data given:
Volume of the gas V1 = 15.9 litres
pressure of the gas P1 = 589 kPa or 5.81 atm.
temperature T1 = 56.5 degrees or 329.3 K
Final pressure P2 = 101.3 kPa
Final temperature T2 = 273 K
At STP the pressure is 1 atm or 101.3 kPa and the temperature is 273 K. So from the question the final temperature and pressure is at STP.
from Gas Law:
=
V2 =
Putting the values in the above rearranged equation of Gas Law:
V2 =
= 76.6 Litres