input: Write a function to return the index of a given value in an array. If the value is present, return its index; if not, return -1.
  assert find_index([2, 5, 9, 15], 5) == 1
  assert find_index([2, 5, 9, 15], 9) == 2
  assert find_index([2, 5, 9, 15], 7) == -1
  assert find_index([], 5) == -1
output: def find_index(arr, value):
      try:
          return arr.index(value)
      except ValueError:
          return -1