input: Write a function to find common elements in two lists.
  assert find_common_elements([1, 2, 3], [3, 4, 5])==[3]
  assert find_common_elements([10, 20, 30], [30, 40, 50])==[30]
  assert find_common_elements([7, 8, 9], [10, 11, 12])==[]
output: def find_common_elements(list1, list2):
      return list(set(list1) & set(list2))