Can you help me with this problem on total pressure?

Question

A sample of He gas (3.0L) at 5.6atm and 25°C was combined with 4.5 L of Ne gas at 3.6 atm and 25°C at constant temperature in a 9.0 L flask. How do I calculate the total pressure in the flask if the inital pressure was 0.00atm

Answer 1

For He:  PV = nRT and n = PV/RT

n = (5.6 atm)(3.0 L)/(0.0821 Latm/Kmol)(298K) = 0.687 moles He

 

For Ne:  PV = nRT and n = PV/RT

n = (3.6 atm)(4.5 L)/(0.0821 Latm/Kmol)(298K) = 0.662 moles Ne

 

Total moles = 0.687 + 0.662 = 1.349 moles

PV = nRT

P = nRT/V

P = (1.349 mol)(0.0821 Latm/Kmol)(298 K)/9.0 L

P = 3.67 atm