The tens and hundreds aren't being printed out. How to do this?

This is my code:

digit = input("Enter a number to convert to words: ")

units = { 1:"one", 2:"two", 3:"three", 4:"four", 5:"five", 6:"six", 7:"seven", 8:"eight", 9:"nine", 10:"ten", 11:"eleven", 12:"twelve", 13:"thirteen", 14:"fourteen", 15:"fifteen", 16:"sixteen", 17:"seventeen", 18:"eighteen",19:"nineteen"}

tens = {

     20:"twenty", 30:"thirty", 40:"fourty", 50:"fifty", 60:"sixty", 70:"seventy", 
     80:"eight", 90:"ninety"}
     

hundred = { 100:"one hundred", 200:"two hundred" }

def number_to_words(problem):

if len(digit) <= 2 and int(digit) in units.keys():
    
     print(units[int(digit)])
        
elif len(digit) == 2:
        
    split_number = []

    for letters in digit:
        split_number.append(letters)

    if len(split_number) == 2:
        
        first_letter = split_number[0] + '0'
        second_letter = split_number[1]

    for num in tens.keys():
        first_letter = int(first_letter)
        if first_letter == num:
            global split_tens
            split_tens = tens[first_letter]

    for num in units.keys():
        second_letter = int(second_letter)
        if second_letter == num:
            global split_unit
            split_unit = units[second_letter]

    print(split_tens,'-', split_unit)

    
if len(digit) == 3:
    split_number = []

    for letters in digit:
        split_number.append(letters)
    
    if len(split_number) == 3:
        first_letter = split_number[0] + "00" 
        second_letter = split_number[1] + "0"
        third_letter = split_number[2]
        # print(first_letter, second_letter, third_letter)

    for num in split_number:
        first_letter = int(first_letter)
        second_letter = int(second_letter)
        # if split_number[1] == int(0):
        #     second_letter = "and"
        third_letter = int(third_letter)
        if first_letter == hundred.keys():
            pass
        if second_letter == tens.keys():
            pass
        if third_letter == units.keys():
            pass
    print(hundred[first_letter], "and", tens[second_letter], units[third_letter])

number_to_words(digit)