input: Write a function to return an array with the running total of numbers in a given list using numpy.
  
  def runningTotal(arr):
      return np.cumsum(arr)
  
  assert np.array_equal(runningTotal([1, 2, 3, 4]), [1, 3, 6, 10])
  assert np.array_equal(runningTotal([5, 10, 15, 20]), [5, 15, 30, 50])
  assert np.array_equal(runningTotal([-1, -2, -3, -4]), [-1, -3, -6, -10])
  assert np.array_equal(runningTotal([3, 5, 7, 9]), [3, 8, 15, 24])
  assert np.array_equal(runningTotal([]), [])
output: def runningTotal(arr):
      return np.cumsum(arr)