input: Write a function to find the highest value in a dictionary.
  assert highestValue({'a': 10, 'b': 20, 'c': 5}) == 20
  assert highestValue({'apple': 25, 'banana': 10, 'cherry': 30}) == 30
  assert highestValue({'x': 1, 'y': 2, 'z': 3}) == 3
output: def highestValue(d):
      return max(d.values())