(define b 810)
(define h 690)

(define tb (- 810 165 275))
(define th 114)

(define opp-berging (* b 100))

(define opp (/ (- (* h b) (* tb th) opp-berging) 10000))
(define verlies 0.07)

(define te-kopen (+ opp (* opp verlies)))