code: def last_boxed_only_string(self, string):
      idx = string.rfind("\\boxed")
      if "\\boxed " in string:
          return "\\boxed " + string.split("\\boxed ")[-1].split("$")[0]
      if idx < 0:
          idx = string.rfind("\\fbox")
          if idx < 0:
              return None
  
      i = idx
      right_brace_idx = None
      num_left_braces_open = 0
      while i < len(string):
          if string[i] == "{":
              num_left_braces_open += 1
          if string[i] == "}":
              num_left_braces_open -= 1
              if num_left_braces_open == 0:
                  right_brace_idx = i
                  break
          i += 1
  
      if right_brace_idx is None:
          retval = None
      else:
          retval = string[idx : right_brace_idx + 1]
  
      return retval
  
imports: import inspect
  import lm_eval.datasets.hendrycks_math.hendrycks_math
  from lm_eval.metrics import mean
  from lm_eval.base import Task, rf
label_desc: Use image node_id 18 for calling the Math obj's underlying member method code with example usage: obj.last_boxed_only_string(string) and returns: retval, unknown, None