The distance a spring stretches from its “free length” is a function of how much tension force is applied to it. The following table gives the spring length y that the given applied force f produced in a particular spring. The spring’s free length is 4.7 in. Find a functional relation between f and x, the extension from the free length (x = y - 4.7).

Force f (lb) ............... Spring length y (in.)
0 ............................................... 4.7
0.94 ......................................... 7.2
2.30 ....................................... 10.6
3.28 ....................................... 12.9