Answer:
199.28 N
Step-by-step explanation:
It is given that,
A spring stretches by 21.0 cm when a 135 N object is attached.
We need to find the weight of a fish that would stretch the spring by 31 cm.
We know that, the force in a spring is given by as per Hooke's law as follows :
F = kx
Where k is spring constant

So, the required weight of a fish is 199.28 N.