Hello everyone! The problem I have is really easy, but something is confusing me. A spring with spring constant 24 N/m is stretched 0.24 m from its equilibrium position. How much work must be done to stretch it an additional 0.072 m? I used the formula : W = (1/2)*k(Xf^2 - Xi^2), (it came out negative) but the answer I get is not the correct one. For Xf I used 0.24+0.072 since that's the distance from the equilibrium position. Can you please give me a hint?