Write index_of(items, x) that returns the index of the first x, or -1 if x is not in the list.
index_of(['a', 'b', 'c'], 'c') → 2
index_of([1, 2], 5) → -1
Submit runs 4 tests, including hidden edge cases.
Each hint gives a little more help. Try on your own first.
Run your code to see the output here.