1. The problem statement, all variables and given/known data A force of 4 lbs is needed to stretch a 10-in. spring 1 inch beyond its natural length. Find the work done in stretching the same spring from its natural length to a length of 15 inches. 2. Relevant equations f=kd W=∫(kx)dx 3. The attempt at a solution So I know that a force of 4lbs is required to stretch a spring 1inch. so 4=1K K=4 I plug K into my work equation and i get ∫(4x)dx I integrate it and get 2x^2 from 0 to 15/12(converting to feet) I plug in my limits of integration and I get 3.125ft-lbs The solution says ~4.167 ft-lbs. I have no idea where I went wrong.