A pen comprises of a spring having a spring constant of 238 N/m. If the tip of the pen is in its retracted position, the spring is compressed 4.20 mm from the unstrained length. In order to push the tip out and lock it into its writing position, the spring should be compressed an extra 6.20 mm. Determine how much work is completed by the spring force to ready the pen for writing? Be sure to comprise the correct algebraic sign with your answer.