input: Write a python function to get the number from a dictionary given its word representation.
  assert get_number_from_word('one')==1
  assert get_number_from_word('five')==5
  assert get_number_from_word('ten')==10
output: def get_number_from_word(word):
      word_to_number = {
          'one': 1,
          'two': 2,
          'three': 3,
          'four': 4,
          'five': 5,
          'six': 6,
          'seven': 7,
          'eight': 8,
          'nine': 9,
          'ten': 10
      }
      return word_to_number.get(word)