Answer:
The value is

Step-by-step explanation:
From the question we are told that
The mass of the cart is m = 0.68 kg
The angle of inclination is

The length of the spring when the cart is a equilibrium is

The length of the spring when at rest is

Generally the weight of the cart is mathematically represented as

=>

=>

Generally the force applied on the spring by the weight of the cart is mathematically represented as

So at equilibrium

=>

=>

=>
