Answer:
The potential energy when it reads 40 N is

Step-by-step explanation:
From the question we are told that
The lowest reading of the spring balance is 0 N and this is at 0 cm = 0 m
The height reading of the spring balance is 60 N and this is at 20 cm = 0.20 m
Generally the length corresponding to the reading of 40 N is mathematically represented as

=>

Generally the potential energy is mathematically represented as

Here
So

=>
