how to know the order of execution?

Question

1- def boo(a,b):
2- a+=2
3- b-=2
4- y=foo(a,b)
5- return y
6- def foo(a,b):
7- y=(a+b)/2
8- return y
9- result=boo(4,6)
10- print(result)

Answer 1

just follow the flow:
you call boo(4,6)
then it calls foo (6,4)
foo returns 5 --- then boo continues and return y (wich was 5).
result is 5