Vapour pressure and solution composition Raoults law

In an ideal solution, the relationship between the partial vapour pressure of a component i in the vapour phase, and the mole fraction of that component in solution, is expressed by Raoult s law as 

Raoult s law is important because it allows the calculation of vapour pressure from a knowledge of the composition of the solution. The requirement of the Montreal Protocol in 1989 for the replacement of chlorofluorocarbon (CFG) propellants in pressurised metered-dose inhalers with hydrofluoroalkanes (HFAs), because of the ozone-depleting 

EXAMPLE 2.2 Calculation of the vapour pressure of a mixture of hydrofluoroalkanes 

Calculate the vapour pressure (in Pa) at 20°C above an aerosol mixture consisting of 30% w/w of HFA 134a (tetrafluoroethane, molecular weight 102) with a vapour pressure of 68.4 psig and 70% w/w of HFA 227 (hepta-fluoropropane, molecular weight 170) with a vapour pressure of 56.0 psig. Assume ideal behaviour. 

For the two propellants HFA 134a and HFA 227 with respective vapour pressures and Ph we have 

---