The restoring force in the spring will be  if it is stretched to a length of
 if it is stretched to a length of  .
.
Further Explanation:
When a spring is we compressed or stretched, there is a force which develops in the spring restoring force of the spring which tends to bring the spring back to normal length.
The restoring force of the spring is expressed as:
 ......(1)
                            ......(1)
Here,  is the force developed in the spring due to stretching,   is the spring constant and
 is the force developed in the spring due to stretching,   is the spring constant and  is the change in length of the spring.
 is the change in length of the spring.

Substitute the values of  and
 and  in equation (1).
 in equation (1).

The restoring force of  is experienced by the spring when the stretched length of the spring should be:
 is experienced by the spring when the stretched length of the spring should be:

Substitute  for
 for  in above expression.
 in above expression.

Therefore, the new length of the spring will be:

Thus, the restoring force in the spring will be  if it is stretched to a length of
 if it is stretched to a length of  .
.
Learn More:
1. How far must you compress a spring with twice the spring constant to store the same amount of energy? brainly.com/question/2114706
2. Max and Maya are riding on a merry-go-round that rotates at a constant speed brainly.com/question/8444623
3. It's been a great day of new, frictionless snow. Julie starts at the top of the 60 brainly.com/question/3943029
Answer Details:
Grade: High School
Subject: Physics
Chapter: Work and energy
Keywords:  Spring, unstretched length, compressed, stretched, restoring force, 3F, 11 cm, F=kx, natural length of spring.