input: Write a function to extract phone numbers that start with '08' from a given list of phone numbers and return them as a new list. If no phone numbers start with '08', return an empty list.
  assert extract_numbers(['0834567', '0945678', '07123456', '08901234', '07890123'])==['0834567', '08901234']
  assert extract_numbers(['0734567', '0945678', '07123456'])==[]
  assert extract_numbers(['0834567', '08901234'])==['0834567', '08901234']
  assert extract_numbers([])==[]
  assert extract_numbers(['0834567', '0734567', '0945678', '08901234'])==['0834567', '08901234']
output: def extract_numbers(phone_numbers):
      return [number for number in phone_numbers if number.startswith('08')]