Is R the gas constant? Cp is heat capacity at constant pressure, the energy required to raise the temperature.
Cp=2R/7. R has units J*K^-1*mol^-1, so it must be molar heat capacity we're talking about here.
Consider the ideal gas equation: PV=nRT. You know P, V and T, so you can solve for nR. The energy required will be
Cp*amount of gas [moles]*number of degrees the temperature is raised, so you get the energy E= 4PV/7T