mechanics of physics

John, of mass 80kg, is standing on a weighing scale in a lift. At a certain instant, the reading of the weighing scale is 600N. Which of the following statements about John at this instant is/are correct?

(2)The force exerted by the weighing scale on John is 200N
(3)John is accelerating downward at a rate of 2.5 ms-2

Ans: (2) - wrong
(3) - correct
問題係:点find " force exerted by the weighing scale on John " and
" acceleration " ?????