input: Write a function to generate an even number between 10 and 200 that is divisible by 5. If no such number is generated within the range, the function should return None.
  assert generate_even_number() in [10, 15, 20, ..., 200]
  assert generate_even_number() % 2 == 0
  assert generate_even_number() % 5 == 0
output: def generate_even_number():
      for num in range(10, 201, 5):
          if num % 2 == 0:
              return num
      return None