Functions as a object

Question

Could someone explain this code? how its work

def add(x, y):
return x + y

def do_twice(func, x, y):
return func(func(x, y), func(x, y))

a = 5
b = 10

print(do_twice(add, a, b))

Answer 1

do_twice(add,5,10)
=> add( add(5,10) , add(5,10) )
=> add( 5+10 , 5+10 )
=> add( 15 , 15 )
=> 15+15
=> 30