It is weigh-in time for the local under-85-kg rugby team. The bathroom scale used to assess eligibility can be described by Hooke's law and is depressed 0.65 cm by its maximum load of 110 kg.

F = kx, where F is the force we apply, k is the spring constant, and x is the extension of the material

so the spring's effective spring constant k is:

k = F / x

k = (110 kg) (9.81 m/s^2) / 0.65 cm

k = 1660 N/cm is the spring's effective spring constant