Answer: 0.00488K
Explanation: using the general gas equation
(P1V1)/T1 =(P2V2)/T1
Substitute
2*6/273= 3*3/T
Simplify
T= 0.00488°K
The enthalpy of an intermediate step should be manipulated when used to produce an overall equation by using the Hess's law. You could multiply the enthalpy by -1 if this equation is reversed in theory.