In the 6th question the temperature at FL 390 is -56.5 as the tropopause starts at 36090ft.
If you use this temp then the Isa dev will be +16 and very close to the answer.
In the first answer the pressure values are supposed to be mugged up.
eg 700hpa - 10000ft
800hpa - 18000ft
300hpa - 30000ft
200 hpa - 39000ft
The rest questions ill figure out and will let u know.