def helper(num1):
    num1 + ""

def add(num1, num2):
    helper(num1)
    return num1 + num2

def double(num):
    return 2 * num

def add_then_double(a, b):
    added = add(a, b)
    doubled = double(added)
    return doubled
    # could have also been written as one line:
    # return double(add(a,b))