I was browsing so site and youtube to understand the PA, DA or ISA Temps Deviation.

Then I got this formula:
Pressure Alt= Elevation + (1013 - QNH) x 30
ISA Temp = 15 - (2 x Elevation/Altitude/1000)

After than i have browsed some website for online test to do some practice and solve some question and I got all good but saw a some question on a forum that i try to solve with question with answer but when i tried to do my answer is not same as their answer.

Example:
What is the ISA Temperature & ISA Deviation if the height is 37,000 feet & is -45 degrees ?
(Ans: -57 degrees for ISA temperature & +12 for ISA deviation)

I used the formula : ISA Temp = 15 - (2 x Elevation/Altitude/1000)
ISA Temp = 15 - (2 x 37000/1000)
ISA Temp = 15 - (2 x 37) = -59 degress
ISA deviation= -45 - -59
ISA deviation= -45 + 59 = +14 degrees

How he get -57 for Isa Temp and +12 for deviation ?

Example 2:
What is the ISA Temperature & ISA Deviation if the height is 57,000 feet & is -67 degrees ?
(His Ans: -57 degrees for ISA temperature & -10 for ISA deviation)

ISA Temp = 15 - (2 x 57000/1000)
ISA Temp = 15 - (2 x 57) = -99degrees
ISA deviation= -67 - -99
ISA deviation= -67 + 99 = +32degrees

How he get -57 for Isa Temp and -10 for ISA deviation ?

The explanation there for Example 1 is:

In the ISA the tropopause is at 36000 feet, where the temperature is –56.25 degrees Celsius (or approximately –57). Above the tropopause the temperature remains constant.

So at 37000 feet the ISA temperature is approximately –57 degrees Celsius.

ISA deviation = Actual Temp – ISA temp

So if actual temp = -45 at 37000 feet then:

ISA deviation = -45 – (-57) = +12

The explanation there for Example 2 is:

(Ans: -57 degrees for ISA temperature & -10 for ISA deviation)

In the ISA the tropopause is at 36000 feet, where the temperature is –56.25 degrees Celsius (or approximately –57). Above the tropopause the temperature remains constant.

So at 37000 feet the ISA temperature is approximately –57 degrees Celsius.

ISA deviation = Actual Temp – ISA temp

So if actual temp = -67 at 36000 feet then:

ISA deviation = -67 – (-57) = -10


But still confuse since the explanation is based on 2 altitude that i don't know how they get it.

Thank for help.

BTW am learning the theory for PPL just got an ideas before I go to do my PPL since I will have to go to south africa and time is money so I start to understand before going