input: Write a function to evaluate a mathematical expression provided as a string.
  assert evaluate_expression("2 + 3 - 5 * 4 + 7 / 6") == -14.833333333333334
  assert evaluate_expression("10 / 2 + 3 * 4 - 5") == 9.0
  assert evaluate_expression("7 * 8 - 6 / 2 + 9") == 64.0
output: def evaluate_expression(expression: str) -> float:
      return eval(expression)