My first question how do he get -57 for Isa Temp and +12 for deviation ? following their explaination above


From what i had understand on the web the temperation from 38 000 ft to 65,500 feet is constant.

My second question is that mean that from 38 000 ft to 65 000ft we don't need to calculate Isa temperation since it is the same -57 degree ?