Use ideal gas law PV=nRT. The pressure, number of moles, and gas constant are unchanged. Rearrange ideal gas law to get n= PV1/RT1= PV2/RT2 now you can cancel out P and R to get V1/T1 = V2/T2 you know V1= 2.55 L, V2= 1.75 L, T2= 16 degC, you can solve for T1( the initial temperature).