Question

What is the restoring force of a spring with a spring constant of 4a and a stretched displacement of 3b?

Answer 1

Here is the correct answer of the given question above. 
The restoring force of a spring with a spring constant of 4a and a stretched displacement of 3b would be -12a/b. 
It is solved using the formula F= -kx. Where x is the displacement and k is the spring constant. F = -(4a)(3b) and you get -12a/b. Hope this answer helps. 

Answer 2

F=-kx

F= - (4a) (3b)

F = -12ab

-kx