calculate_time

def calc(length, use):
  if use == 10:
    speed = 120
  elif use == 11:
    speed = 80
  elif use == 20 or use == 21:
    speed = 90
  elif use == 22 or use == 30 or use == 31 or use == 32:
    speed = 50
  elif use == 40 or use == 50:
    speed = 30
  else:
    speed = 30
    
  #go back to meters  
  speed = speed * 1000
  
  time = length /speed
  
  #transform into minutes
  time = time * 60
  
  return time