input: def find_index(arr: List[int], x: int) -> int:
      """ Find the index of the given value in the array.
      Return -1 if the value is not present in the array.
      >>> find_index([2, 5, 9, 15], 5)
      1
      >>> find_index([2, 5, 9, 15], 7)
      -1
      """
output:     for i in range(len(arr)):
          if arr[i] == x:
              return i
      return -1