input: Write a function to find the first number divisible by 7 in an array.
  assert findFirstDivisibleBy7([41, 42, 43, 44, 45]) == 42
  assert findFirstDivisibleBy7([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 14]) == 7
  assert findFirstDivisibleBy7([10, 20, 30, 40, 50]) == -1
output: def findFirstDivisibleBy7(arr):
      for num in arr:
          if num % 7 == 0:
              return num
      return -1