input: Write a python function to find the index of a number in an array.
  assert findIndex([1,3,7,9,0,4], 7) == 2
  assert findIndex([5,8,6,1,4,2], 4) == 4
  assert findIndex([2,3,5,7,11,13], 11) == 4
  assert findIndex([10,20,30,40,50], 25) == -1
output: def findIndex(arr, num):
      try:
          return arr.index(num)
      except ValueError:
          return -1