How Do You Calculate the Force Constant of a Spring?

[treeelf5150]

I'm jut not sure how to solve this problem in general, I tried a couple ways, but I keep getting wrong answers and I only have 2 attempts left. Please give me a direction to go in!

A spring is 17.1cm long when it is lying on a table. One end is then attached to a hook and the other end is pulled by a force that increases to 25.5N , causing the spring to stretch to a length of 19.5cm .
What is the force constant of this spring?

First I drew the FBD, summed the forces and normal force and gravity cancel, then youre left with a force of 25N in the positive direction, its not accelerating so it equals zero. Thats all my teacher has taught me about force problems, we haven't even talked about springs before. I know that the answer should be in N/m from, so I tried dividing the force by the total length, and it was wrong. I then divided the force by the difference in lengths, which still was wrong. Unfortunately my teacher doesn't help us with our homework and isn't a good teacher in general for teaching... Please help me understand :(

 

[Chestermiller]

Show us your numbers when you divide by the change in length.

Also, in the future, please use the homework template. Otherwise, future posts will be deleted.

Chet

 

[treeelf5150]

I'm sorry, I wasn't aware there was a emplate, I'm using my phone and the whole page isn't loading. I have found the answer to the problem, my mistake was not converting from centimeters to meters before hand. Thank you for replying though and I will get on my computer to see how the template is