Multiply items in list

I am trying to write a function (for academic reasons) that multiply every number in this list : list = [[6 , [1, 2, 3]] I have tried this solution:

def grow(arr):
    for num in arr:
        x = num
        x * num
        for value in num:
            y = value * num
        return y * x   

But I keep getting: TypeError: 'int' object is not iterable someone help me understand please. The expected output should be: 36

Read more here: https://stackoverflow.com/questions/66344838/multiply-items-in-list