Trypanomic problem!

Classical Mechanics Level 5

In the figure , three $10000$ kg ore cars are held at rest on a mine railway using a cable that is parallel to the rails, which are inclined at angle $\theta = 30°$ . The cable stretches $15$ cm just before the coupling between the longer two cars breaks, detaching the lowest car . Assuming that the cable obeys Hooke’s law, find the amplitude (in meters) of the resulting oscillations of the remaining two cars.