From the context of the first paragraph it is the latter (we have a mass which weighs 8 pounds, but a weight is a force so our unit of mass is the slug), so then we are using slugs as our unit of farce.
So for our spring we get:
That is the extension in feet is the spring constant times the load in pounds force and so ft per pound force.
Now from the statement of the problem if is the displacement from the equilibrium extension the force on the load is:
This is equal to the mass (that is slugs) times the acceleration so:
(pheww.. and I hope I have the units right! Please suggest to you teacher that they update their text/s and teaching to use SI (mks) units)