input: Write a python function to calculate the sum of all elements in a 2D list.
  assert calculate_total([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) == 45
  assert calculate_total([[0, 0, 0], [0, 0, 0], [0, 0, 0]]) == 0
  assert calculate_total([[1, -1, 1], [-1, 1, -1], [1, -1, 1]]) == 0
output: def calculate_total(matrix):
      return sum(sum(row) for row in matrix)