In a mixture of methane (CH4) and air there are three volumes of oxygen to one volume of methane. From initial conditions of 1 bar and 95°C the gas is compressed reversibly and adiabatically through a volume ratio of 5. Assuming that air contains only oxygen and nitrogen, calculate: (i) the values of cp, C₁, čp, č₁, R and y for the mixture; (ii) the final pressure and temperature of the mixture; (iii) the work input per unit mass of mixture.