For a fixed mass of gas we can use the combined gas law.
(P1V1)/T1 = (P2V2)/T2
where P1 is pressure , T1 is temperature and V1 is volume at the first instance
and P2 is standard pressure and T2 is standard temperature and V2 is the volume at STP conditions
temperatures at both instances should be in kelvin scale
T1 - 30 °C + 273.15 = 303.15 K
T2 - 273.15 K
substituting the values in the equation
(2.3 atm x 2.2 L) / 303.15 K = (1.0 atm x V2) / 273.15 K
V2 = 4.6 L
the volume at STP is 4.6 L
