A spring-mounted machine with a mass of 24 kg is observed to vibrate harmonically in the vertical direction with an amplitude of 0.30 mm under the action of a vertical force which varies harmonically between F₀ and −F₀ with a frequency of 4 Hz. Damping is negligible. If a static force of magnitude F₀ causes a deflection of 0.60 mm, calculate the equivalent spring constant k for the springs which support the machine.