A man who weights 900 N stands on a platform scale in a elevator the elevator has made 4000 kg the reading on the scale is 700 N

a = -2.17 m / s²

Explanation:

In this problem you must ask for the acceleration of the elevator.

Let's use Newton's second law

           F-W = ma

           a = F / m-g

the weight of the body is 900 N and the force is the reading of the scale, let's find the mass

         w = mg

         m = w / g

         m = 900 / 9.8

         m = 91.84 kg

let's calculate

         a = 700 / 91.84 - 9.8

         a = -2.17 m / s²

The negative sign indicates that the elevator is going down