(define T (list (list 11 12 13 14 15)
                (list 21 22 23 24 25)
                (list 31 32 33 34 35) ))

(define empty-table '())


(define (last x)
  (if (null? (cdr x)) x
      (last (cdr x))))

(define (append! x y)
  (begin (set-cdr! (last x) y)
         x))

(define (sum l)
  (if (null? l) 0
      (+ (car l)(sum (cdr l)))))

(define (sumlists l1 l2)
  (if (null? l1) l2
      (append (list (+ (car l1) (car l2))) (sumlists (cdr l1) (cdr l2)))))

(define (sumcols T)
  (if (null? T) T
      (sumlists(sumlists (car T) (cadr T)) ((sumcols (cddr T)) ))))

(define (process-rows! T)
  (cond ((null? T) T)
        (else (append! (car T) (list(sum (car T)))) (process-rows! (cdr T)))))

(define (process-cols! T)
  (cond ((null? T) T)
        (else (append! T (sumcols T)))))