Mechanic used wrench to compress by x = 10 cm, and then fully decompress the spring?

Question

http://i4.tinypic.com/6ut59xe.gif

Mechanical works done by the mechanic were respectively
A1 = +300J
A2 = +200J

What is spring constant K of the spring?

Answer 1

A1 = A(friction) + A(spring)
A2 = A(friction) - A(spring)
A(spring) = 50 J = kx^2/2 = 0.005k
k = 10000 N/m

Answer 2

Here:

Here I found a shortcut and I think it works better.

300J-200J=100J

PE in the spring is 100J

U=1/2kx^2

2U/x^2=k

2(100)/0.1m^2=200/0.01

k=20000N/m

Seems to be 20000 is a big number.