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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def CalculateForecastStats(matched, available, possible=None):
 """Calculate forecast percentage stats. Args: matched: The number of matched impressions. available: The number of available impressions. possible: The optional number of possible impressions. Returns: The percentage of impressions that are available and possible. """

  if matched > 0:
    available_percent = (float(available) / matched) * 100.
  else:
    available_percent = 0

  if possible is not None:
    if matched > 0:
      possible_percent = (possible/float(matched)) * 100.
    else:
      possible_percent = 0
  else:
    possible_percent = None

  return available_percent, possible_percent