A 100-kg machine operates at \(1400 \mathrm{rpm}\) and produces a harmonic force of magnitude \(80,000 \mathrm{~N}\). The magnitude of the force transmitted to the foundation is to be reduced to \(20,000 \mathrm{~N}\) by mounting the machine on four identical undamped isolators in parallel. What is the minimum stiffness of each isolator?