 Problem Statement

I have had a go at the following question but have gone wrong somewhere, any ideas?
A mass of 0.12 kg of air has an initial temperature of 500°C and pressure 0.8 MPa. If the air is
expanded according to the law pV1.2 = c to a final volume of 90 litres, determine
i) its initial volume,
ii) its final pressure,
iii) its final temperature.
For air, take R = 287 Jkgˉ¹ Kˉ¹.
 Relevant Equations

pV = mRT
V = mRT/P
T = PV/mR
Mass = 0.12kg
Initial temp = 500°c = 773K
Initial pressure = 0.8 MPa = 800,000 Pa
Final volume = 90L
R = 287 Jkg^1K^1
1) Initial Volume
V=mRT/P
0.12 x 287 x 773 / 800,000 = 26,662.12m^3
2) Final Pressure
P2 = P1P2^1.2/V2^1.2
800,000 x 26,662.12^1.2 / 90 = 1,816,095,330 Pa = 1,816 MPa
3) Final Temperature
T=P2V2^1.2/mR
1,816,095,330 x 90 / 0.12 x 287 = 1,291 x 10^11 K
Initial temp = 500°c = 773K
Initial pressure = 0.8 MPa = 800,000 Pa
Final volume = 90L
R = 287 Jkg^1K^1
1) Initial Volume
V=mRT/P
0.12 x 287 x 773 / 800,000 = 26,662.12m^3
2) Final Pressure
P2 = P1P2^1.2/V2^1.2
800,000 x 26,662.12^1.2 / 90 = 1,816,095,330 Pa = 1,816 MPa
3) Final Temperature
T=P2V2^1.2/mR
1,816,095,330 x 90 / 0.12 x 287 = 1,291 x 10^11 K