input: Write a function to calculate the sum of all elements in a list of integers that are divisible by 3. If the list is empty then return 0.
  
  assert divisibleBy3([4, 6, 17, 24, 5, 9])==39
  assert divisibleBy3([3, 5, 7, 8])==3
  assert divisibleBy3([12, 6, 9, 30])==57
  assert divisibleBy3([])==0
output: def divisibleBy3(lst):
      return sum(x for x in lst if x % 3 == 0)