Need to find the spring constant

[christianhood]

Homework Statement

A series of masses are hung from a vertical spring and the length is measured in each case to the nearest milimeter. Data below:

Mass : Spring Length
050g : 40.2cm
100g : 45.8cm
150g : 50.9cm
200g : 56.4cm
250g : 61.4cm
300g : 66.9cm
350g : 73.7cm
400g : 81.2cm

I need to find the spring constant.

Homework Equations

F_s = k | l - l₀| ,
where
F_s = Spring Force
k = spring constant
l = length of spring
l₀ = initial length of spring

The Attempt at a Solution

I know that F_s = F_g = mass / 100 (using g = 10 N/kg).
I just don't know how to get the constant because I don't know what the initial spring length is (it's not 0).

 

[AEM]

Think about the equation F = kX for a moment. What kind of graph does that make? What one of those letters represents the slope of that graph?

Can you put those hints together to figure out a way to determine the spring constant?

 

[christianhood]

Think about the equation F = kX for a moment. What kind of graph does that make? What one of those letters represents the slope of that graph?

Can you put those hints together to figure out a way to determine the spring constant?

Oh, okay. It's the same for any initial length. Thanks :)