The diagram below represents the graph of the force applied in stretching a spiral spring against the corresponding extension produced within its elastic li...

The diagram below represents the graph of the force applied in stretching a spiral spring against the corresponding extension produced within its elastic limit.

Using the notations on the graph, determine the:

(a) force constant of the spring;

(b) work done in stretching the spring from 10 x 10\(^{-2}\)m to 20 x 10\(^{-2}\)m.