[racket] Implementing an equal? method for a class

Okay, this is really a newbie question, but here goes. I have a class that represents a Sudoku grid. Internally, the grid is stored as a vector of vectors of integers:

(define simple-grid%
  (class object%
    
    (super-new)
    
    ;b is an internal representation of the grid and is initialized to an empty grid
    (define b(make-vector 9 (make-vector 9 0)))
    
    (define/public (get-cell r c)
      (let
          ([row (vector-ref b (sub1 r))])
        (vector-ref row (sub1 c))))

     ;etc.


I provide methods get-cell to retrieve the contents of a single cell, set-cell! to (destructively) update the contents of a cell and so forth. In principle, I could implement equal? by looping all 81 cells and comparing them one by one, but this seems awkward. It seems like I ought to be able to just check that the state vectors are equal? but I have no access to b outside the class. In Java, I'd add a protected method getStateVector that could be called from within a separate method named equalTo that tells me if a grid object g1 is equivalent to a g2. Or at least I could do this. I really don't want to expose how the internal representation of the grid to other classes. Then again, maybe that's Java thinking in the context of Racket.