A pen contains a spring by a spring constant of 200 N/m. When the tip of the pen is in its retracted position, the spring is compressed 5.90 mm from its unstrained length. In order to push the tip out and lock it into its writing position, the spring should be compressed an additional 6.20 mm. How much work is done by the spring force to ready the pen for writing? Be sure to include the proper algebraic sign with your answer.