텍스트 숫자 더하기를 빼기로 바꺼 주시면 안될까요??

;—————————————————————————————–
;;*** PLUS & SUM
(defun C:SUM (/ b1 b2 b3 b4 tot pot total)
     (setvar “cmdecho” 0)
     (graphscr)
     (setq n 0 t 0
           ss (ssget ‘((-4 . “<or”)(0 . “TEXT”)(0 . “MTEXT”)(-4 . “or>”)))
           en (sslength ss)
     )
     (while (< n en)
            (setq ename (ssname ss n)
                  elist (entget ename)
                  no (atof (cdr (assoc 1 elist) ) )
                  sum (+ t no)
                  t sum
                  n (+ n 1)
            )
     )
     (setq pot (getint “Decimal point <0 to 8> : “)
           total (rtos t 2 pot))
     (prompt (strcat “nTotal = ” total )) (terpri)
     (setq tot (entsel “Pick a change on target text”))(terpri)
     (setq b1 (entget (car tot)))
     (setq b2 (assoc 1 b1))
     (setq b3 (cons (car b2) total))
     (setq b4 (subst b3 b2 b1))
     (entmod b4)
 (princ “*** 계산이 완료되었습니다. ***”)

이리습 빼기도 있었으면 조을껏 같아요 ^^*
도와주세요