At 45 C the volume of a certain gas is 27.5 L

Regretfully, I do not know what is asked of the problem because it is not stated above. However, it is easier to answer any question pertaining to the temperature, volume, and pressure of gases by assuming that they behave ideally. With this, we'll be able to use the ideal gas law which is mathematically expressed as,

PV = nRT

where P and V are pressure and volume, respectively. n is the amount of material in mol, R is gas constant, and T is temperature.