Spring Stretching

Consider a helical compression spring has a free length of 5 inches and a spring constant of 300 lb/in. What force (lb) is required to stretch the spring to a length of 8 inches?

Expand Hint
The force in a spring is:
$$$F_s=k\delta $$$
where $$k$$ is the spring constant, and $$\delta$$ is the change in spring length from the un-deformed spring length.
Hint 2
$$$\delta=stretched\:length-free\:length$$$
The force in a spring is:
$$$F_s=k\delta $$$
where $$k$$ is the spring constant, and $$\delta$$ is the change in spring length from the un-deformed spring length.

Since $$\delta=stretched\:length-free\:length=8in-5in=3\:in$$ , the required force is:
$$$F_s=(300\frac{lb}{in})(3in)=900\:lb$$$
900 lb