33000 feet at 2 per thousand feet = 66.
Starting at +15 on the surface means the temp should be -51, which is logical, given that it's supposed to be -56.5 at 36 090 feet.
But it's ISA +15 so add it back......
Looks like one of those questions where they include false information.
Last edited by paco; 22nd April 2017 at 05:52.