Recall that in the equilibrium position, the upward force of the spring balances the force of gravity on the weight. Use this concept, along with the variable mass value, the ruler, and the moveable line, to estimate the spring constant k of the spring. Set the damping to "Lots" so that the mass will come to rest quickly after being changed, and make sure the gravity is set to "Earth." Finally, set the spring constant to "Small." Estimate the spring constant several times (using different values of mass) and average together for the most accurate calculation. Express your answer in N/m to two significant figures.