text: s^2 = 5L\nL = s^2/5 =65*65/5 = 65*13 = 650 + 130 + 65 (fast reckoning) = 845 feet\n\n---\n\nIn fact I am not so easy with miles and feet:\nI know it by km as they teach in Italy:\nlenght of stop = approx. (speed/10)^2\n\nso\nspeed = sqrt(lenght)*10\nlenght in km; speed in km/h