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 was produced in a particular spring by the given applied force f. 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