input: Write a function to find the largest number divisible by three in a list.
  assert divisibleByThree([8, 5, 12, 15, 9]) == 15
  assert divisibleByThree([1, 2, 3, 4, 5, 6]) == 6
  assert divisibleByThree([10, 20, 30, 40, 50]) == 30
output: def divisibleByThree(lst):
      divisible_numbers = [num for num in lst if num % 3 == 0]
      return max(divisible_numbers) if divisible_numbers else None