The train engine and its four boxcars are coasting at 40 m/s. The engine train has mass of 5500 kg and the boxcars have masses, from left to right, of 1000 kg, 1500 kg, 2000 kg, and 3000 kg. If the train can shoot boxcars backwards at 30 m/s relative to the train's speed, how many boxcars does the train need to shoot out in order to obtain a speed of 58.75 m/s?

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